[pacman-dev] [PATCH 1/2] pacman: fix possible buffer overflow

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[pacman-dev] [PATCH v2] libalpm:...

morganamilo

22 Sep 2018 22 Sep '18

1:16 p.m.

in the function query_fileowner, if the user enters a string longer than PATH_MAX then rpath will buffer overflow when lrealpath tries to strcat everything together. Even if we made sure filename was never longer than PATH_MAX this would not help because lrealpath may concatenate filename with the current directory among other things. So simply let lrealpath calculate the size needed and allocate it for us. This also fixes the compiler warning; query.c: In function ‘query_fileowner’: query.c:192:4: warning: ‘strncpy’ specified bound 4096 equals destination size [-Wstringop-truncation] strncpy(rpath, filename, PATH_MAX); The warning could have also been Fixed by using PATH_MAX -1 and explicitly terminating the string. However this would not fix the buffer overflow. Signed-off-by: morganamilo diff --git a/src/pacman/query.c b/src/pacman/query.c index 00c39638..a1197cea 100644 --- a/src/pacman/query.c +++ b/src/pacman/query.c @@ -155,10 +155,10 @@ static int query_fileowner(alpm_list_t *targets) for(t = targets; t; t = alpm_list_next(t)) { char *filename = NULL; - char rpath[PATH_MAX], *rel_path; + char *rpath = NULL, *rpathsave, *rel_path; struct stat buf; alpm_list_t *i; - size_t len; + size_t len, rlen; unsigned int found = 0; int is_dir = 0, is_missing = 0; @@ -187,9 +187,15 @@ static int query_fileowner(alpm_list_t *targets) } } - if(!lrealpath(filename, rpath)) { + if(!(rpath = lrealpath(filename, NULL))) { /* Can't canonicalize path, try to proceed anyway */ - strncpy(rpath, filename, PATH_MAX); + rpath = strdup(filename); + } + + rlen = strlen(rpath); + if(rlen + 1 >= PATH_MAX) { + pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); + goto targcleanup; } if(strncmp(rpath, root, rootlen) != 0) { @@ -201,11 +207,14 @@ static int query_fileowner(alpm_list_t *targets) rel_path = rpath + rootlen; if((is_missing && is_dir) || (!is_missing && (is_dir = S_ISDIR(buf.st_mode)))) { - size_t rlen = strlen(rpath); if(rlen + 2 >= PATH_MAX) { pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); goto targcleanup; } + if ((rpathsave = realloc(rpath, rlen + 2)) == NULL) { + goto targcleanup; + } + rpath = rpathsave; strcat(rpath + rlen, "/"); } -- 2.19.0

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morganamilo

22 Sep 22 Sep

1:16 p.m.

New subject: [pacman-dev] [PATCH 2/2] pacman: give path too long error after strcat

The string only becomes longer than PATH_MAX once adding "/" to the end. The error message should give this version of the path. Signed-off-by: morganamilo diff --git a/src/pacman/query.c b/src/pacman/query.c index a1197cea..ecf8d148 100644 --- a/src/pacman/query.c +++ b/src/pacman/query.c @@ -207,15 +207,15 @@ static int query_fileowner(alpm_list_t *targets) rel_path = rpath + rootlen; if((is_missing && is_dir) || (!is_missing && (is_dir = S_ISDIR(buf.st_mode)))) { - if(rlen + 2 >= PATH_MAX) { - pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); - goto targcleanup; - } if ((rpathsave = realloc(rpath, rlen + 2)) == NULL) { goto targcleanup; } rpath = rpathsave; strcat(rpath + rlen, "/"); + if(rlen + 2 >= PATH_MAX) { + pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); + goto targcleanup; + } } for(i = packages; i && (!found || is_dir); i = alpm_list_next(i)) { -- 2.19.0

Andrew Gregory

1:54 p.m.

New subject: [pacman-dev] [PATCH 2/2] pacman: give path too long error after strcat

On 09/22/18 at 09:16pm, morganamilo wrote:

...

The string only becomes longer than PATH_MAX once adding "/" to the end. The error message should give this version of the path.

Signed-off-by: morganamilo

NACK. The trailing slash is in the format string; your version now has two trailing slashes..

...

diff --git a/src/pacman/query.c b/src/pacman/query.c index a1197cea..ecf8d148 100644 --- a/src/pacman/query.c +++ b/src/pacman/query.c @@ -207,15 +207,15 @@ static int query_fileowner(alpm_list_t *targets) rel_path = rpath + rootlen;

if((is_missing && is_dir) || (!is_missing && (is_dir = S_ISDIR(buf.st_mode)))) { - if(rlen + 2 >= PATH_MAX) { - pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); - goto targcleanup; - } if ((rpathsave = realloc(rpath, rlen + 2)) == NULL) { goto targcleanup; } rpath = rpathsave; strcat(rpath + rlen, "/"); + if(rlen + 2 >= PATH_MAX) { + pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); + goto targcleanup; + } }

for(i = packages; i && (!found || is_dir); i = alpm_list_next(i)) { -- 2.19.0

Morgan Adamiec

1:56 p.m.

New subject: [pacman-dev] [PATCH 2/2] pacman: give path too long error after strcat

On Sat, 22 Sep 2018 at 21:54, Andrew Gregory wrote:

...

On 09/22/18 at 09:16pm, morganamilo wrote:

...
The string only becomes longer than PATH_MAX once adding "/" to the end. The error message should give this version of the path.

Signed-off-by: morganamilo

NACK. The trailing slash is in the format string; your version now has two trailing slashes..

...
diff --git a/src/pacman/query.c b/src/pacman/query.c index a1197cea..ecf8d148 100644 --- a/src/pacman/query.c +++ b/src/pacman/query.c @@ -207,15 +207,15 @@ static int query_fileowner(alpm_list_t *targets) rel_path = rpath + rootlen;

if((is_missing && is_dir) || (!is_missing && (is_dir = S_ISDIR(buf.st_mode)))) { - if(rlen + 2 >= PATH_MAX) { - pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); - goto targcleanup; - } if ((rpathsave = realloc(rpath, rlen + 2)) == NULL) { goto targcleanup; } rpath = rpathsave; strcat(rpath + rlen, "/"); + if(rlen + 2 >= PATH_MAX) { + pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); + goto targcleanup; + } }

for(i = packages; i && (!found || is_dir); i = alpm_list_next(i)) { -- 2.19.0

Oh yeah silly me, missed the / inside the printf. Disregard this patch then.

Andrew Gregory

2:20 p.m.

On 09/22/18 at 09:16pm, morganamilo wrote:

...

in the function query_fileowner, if the user enters a string longer than PATH_MAX then rpath will buffer overflow when lrealpath tries to strcat everything together.

Even if we made sure filename was never longer than PATH_MAX this would not help because lrealpath may concatenate filename with the current directory among other things.

So simply let lrealpath calculate the size needed and allocate it for us.

This also fixes the compiler warning; query.c: In function ‘query_fileowner’: query.c:192:4: warning: ‘strncpy’ specified bound 4096 equals destination size [-Wstringop-truncation] strncpy(rpath, filename, PATH_MAX);

The warning could have also been Fixed by using PATH_MAX -1 and explicitly terminating the string. However this would not fix the buffer overflow.

Signed-off-by: morganamilo

diff --git a/src/pacman/query.c b/src/pacman/query.c index 00c39638..a1197cea 100644 --- a/src/pacman/query.c +++ b/src/pacman/query.c @@ -155,10 +155,10 @@ static int query_fileowner(alpm_list_t *targets)

for(t = targets; t; t = alpm_list_next(t)) { char *filename = NULL; - char rpath[PATH_MAX], *rel_path; + char *rpath = NULL, *rpathsave, *rel_path; struct stat buf; alpm_list_t *i; - size_t len; + size_t len, rlen; unsigned int found = 0; int is_dir = 0, is_missing = 0;

@@ -187,9 +187,15 @@ static int query_fileowner(alpm_list_t *targets) } }

- if(!lrealpath(filename, rpath)) { + if(!(rpath = lrealpath(filename, NULL))) { /* Can't canonicalize path, try to proceed anyway */ - strncpy(rpath, filename, PATH_MAX); + rpath = strdup(filename); + } + + rlen = strlen(rpath); + if(rlen + 1 >= PATH_MAX) { + pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); + goto targcleanup; }

if(strncmp(rpath, root, rootlen) != 0) { @@ -201,11 +207,14 @@ static int query_fileowner(alpm_list_t *targets) rel_path = rpath + rootlen;

if((is_missing && is_dir) || (!is_missing && (is_dir = S_ISDIR(buf.st_mode)))) { - size_t rlen = strlen(rpath); if(rlen + 2 >= PATH_MAX) { pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), rpath); goto targcleanup; } + if ((rpathsave = realloc(rpath, rlen + 2)) == NULL) { + goto targcleanup; + } + rpath = rpathsave; strcat(rpath + rlen, "/"); }

-- 2.19.0

Good catch, but this approach allows lrealpath to allocate a buffer larger than PATH_MAX only to error if it actually does. lrealpath is intended to be the same as realpath (aside from not resolving symlinks obviously), so it should be fixed so that it doesn't write more than PATH_MAX into a provided buffer. We could switch to dynamic allocation in addition to fixing lrealpath, but then the PATH_MAX checks would be pointless and should be removed. You also never free the malloc'd path. You can run the entire test suite under valgrind with `make PY_TEST_FLAGS=--valgrind check` to catch most memory leaks. apg

Morgan Adamiec

2:46 p.m.

On Sat, 22 Sep 2018 at 22:20, Andrew Gregory wrote:

...

Good catch, but this approach allows lrealpath to allocate a buffer larger than PATH_MAX only to error if it actually does. lrealpath is intended to be the same as realpath (aside from not resolving symlinks obviously), so it should be fixed so that it doesn't write more than PATH_MAX into a provided buffer.

I tried this initially, not really being that familiar with C I couldn't really figure it out. How exactly would one communicate the error? I can return null but then that could be anything. I could also move the alpm_log_error into lrealpath but just seems messy. Maybe just truncate and don't error?

...

We could switch to dynamic allocation in addition to fixing lrealpath, but then the PATH_MAX checks would be pointless and should be removed.

I assumed PATH_MAX was an OS limit type of thing, so even if we had a bigger buffer it would be useless as it would not work properly with other functions. I'm guessing that's not the case?

...

You also never free the malloc'd path. You can run the entire test suite under valgrind with `make PY_TEST_FLAGS=--valgrind check` to catch most memory leaks.

apg

I did free it at some point. Must have accidentally checked it out at some point. Whoops

Andrew Gregory

2:57 p.m.

On 09/22/18 at 10:46pm, Morgan Adamiec wrote:

...

On Sat, 22 Sep 2018 at 22:20, Andrew Gregory wrote:

...
Good catch, but this approach allows lrealpath to allocate a buffer larger than PATH_MAX only to error if it actually does. lrealpath is intended to be the same as realpath (aside from not resolving symlinks obviously), so it should be fixed so that it doesn't write more than PATH_MAX into a provided buffer.

I tried this initially, not really being that familiar with C I couldn't really figure it out. How exactly would one communicate the error? I can return null but then that could be anything. I could also move the alpm_log_error into lrealpath but just seems messy. Maybe just truncate and don't error?

Set errno to ENAMETOOLONG and return NULL, just like realpath.

...

...
We could switch to dynamic allocation in addition to fixing lrealpath, but then the PATH_MAX checks would be pointless and should be removed.

I assumed PATH_MAX was an OS limit type of thing, so even if we had a bigger buffer it would be useless as it would not work properly with other functions. I'm guessing that's not the case?

Sort of. Path limitations are pretty messy, but yes, some functions will not work correctly with paths longer than PATH_MAX. We don't actually use the path after resolving it though; we just do a partial comparison against paths stored in pacman's database.

...

...
You also never free the malloc'd path. You can run the entire test suite under valgrind with `make PY_TEST_FLAGS=--valgrind check` to catch most memory leaks.

I did free it at some point. Must have accidentally checked it out at some point. Whoops

Morgan Adamiec

3:18 p.m.

On Sat, 22 Sep 2018 at 22:57, Andrew Gregory wrote:

...

Set errno to ENAMETOOLONG and return NULL, just like realpath.

The problem still remains. You can input a filename that's < PATH_MAX and have it resolve to something > PATH_MAX. You have no way to print what that resolved path was. You can print the original file name but that could be misleading. Although I guess the chances of any one running into that is pretty tiny. So the solution might just be to not care and print the original filename. I'll make a patch for it, see what people think.

morganamilo

3:30 p.m.

New subject: [pacman-dev] [PATCH v2] pacman: fix possible buffer overflow

in the function query_fileowner, if the user enters a string longer than PATH_MAX then rpath will buffer overflow when lrealpath tries to strcat everything together. So make sure to bail early if the generated path is going to be bigger than PATH_MAX. This also fixes the compiler warning: query.c: In function ‘query_fileowner’: query.c:192:4: warning: ‘strncpy’ specified bound 4096 equals destination size [-Wstringop-truncation] strncpy(rpath, filename, PATH_MAX); Signed-off-by: morganamilo diff --git a/src/pacman/query.c b/src/pacman/query.c index 00c39638..c661fafb 100644 --- a/src/pacman/query.c +++ b/src/pacman/query.c @@ -102,7 +102,7 @@ static char *lrealpath(const char *path, char *resolved_path) { const char *bname = mbasename(path); char *rpath = NULL, *dname = NULL; - int success = 0; + int success = 0, len; if(strcmp(bname, ".") == 0 || strcmp(bname, "..") == 0) { /* the entire path needs to be resolved */ @@ -115,8 +115,14 @@ static char *lrealpath(const char *path, char *resolved_path) if(!(rpath = realpath(dname, NULL))) { goto cleanup; } + + len = strlen(rpath) + strlen(bname) + 2; + if (len > PATH_MAX) { + errno = ENAMETOOLONG; + goto cleanup; + } if(!resolved_path) { - if(!(resolved_path = malloc(strlen(rpath) + strlen(bname) + 2))) { + if(!(resolved_path = malloc(len))) { goto cleanup; } } @@ -187,11 +193,16 @@ static int query_fileowner(alpm_list_t *targets) } } + errno = 0; if(!lrealpath(filename, rpath)) { + if (errno == ENAMETOOLONG) { + pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), filename); + goto targcleanup; + } /* Can't canonicalize path, try to proceed anyway */ - strncpy(rpath, filename, PATH_MAX); + strncpy(rpath, filename, PATH_MAX - 1); + rpath[PATH_MAX - 1] = '\0'; } - if(strncmp(rpath, root, rootlen) != 0) { /* file is outside root, we know nothing can own it */ pm_printf(ALPM_LOG_ERROR, _("No package owns %s\n"), filename); -- 2.19.0

Andrew Gregory

16 Oct 16 Oct

7:09 p.m.

New subject: [pacman-dev] [PATCH v2] pacman: fix possible buffer overflow

On 09/22/18 at 11:30pm, morganamilo wrote:

...

in the function query_fileowner, if the user enters a string longer than PATH_MAX then rpath will buffer overflow when lrealpath tries to strcat everything together.

So make sure to bail early if the generated path is going to be bigger than PATH_MAX.

This also fixes the compiler warning: query.c: In function ‘query_fileowner’: query.c:192:4: warning: ‘strncpy’ specified bound 4096 equals destination size [-Wstringop-truncation] strncpy(rpath, filename, PATH_MAX);

Signed-off-by: morganamilo

diff --git a/src/pacman/query.c b/src/pacman/query.c index 00c39638..c661fafb 100644 --- a/src/pacman/query.c +++ b/src/pacman/query.c @@ -102,7 +102,7 @@ static char *lrealpath(const char *path, char *resolved_path) { const char *bname = mbasename(path); char *rpath = NULL, *dname = NULL; - int success = 0; + int success = 0, len;

if(strcmp(bname, ".") == 0 || strcmp(bname, "..") == 0) { /* the entire path needs to be resolved */ @@ -115,8 +115,14 @@ static char *lrealpath(const char *path, char *resolved_path) if(!(rpath = realpath(dname, NULL))) { goto cleanup; } + + len = strlen(rpath) + strlen(bname) + 2; + if (len > PATH_MAX) { + errno = ENAMETOOLONG; + goto cleanup; + } if(!resolved_path) { - if(!(resolved_path = malloc(strlen(rpath) + strlen(bname) + 2))) { + if(!(resolved_path = malloc(len))) { goto cleanup; } } @@ -187,11 +193,16 @@ static int query_fileowner(alpm_list_t *targets) } }

+ errno = 0;

No need to explicitly set errno here. lrealpath should always set it on failure.

...

if(!lrealpath(filename, rpath)) { + if (errno == ENAMETOOLONG) { + pm_printf(ALPM_LOG_ERROR, _("path too long: %s/\n"), filename); + goto targcleanup; + } /* Can't canonicalize path, try to proceed anyway */ - strncpy(rpath, filename, PATH_MAX); + strncpy(rpath, filename, PATH_MAX - 1); + rpath[PATH_MAX - 1] = '\0';

This silences the warning, but filename could still be longer than PATH_MAX, in which case the results will be incorrect. I think the best thing to do is treat ENAMETOOLONG the same as any other lrealpath error, and explicitly check if strlen(filename) >= PATH_MAX instead.

...

} -

Please leave this empty line to separate the two blocks.

...

if(strncmp(rpath, root, rootlen) != 0) { /* file is outside root, we know nothing can own it */ pm_printf(ALPM_LOG_ERROR, _("No package owns %s\n"), filename); -- 2.19.0

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