path: root/sha1_file.c
diff options
authorJim Meyering <>2007-07-03 10:40:20 (GMT)
committerJunio C Hamano <>2007-07-03 19:25:29 (GMT)
commit9cb18f56fdee6885884f5f08bd5335a42d9034dc (patch)
tree9af06f4ef04c75a07edeb652255c63b084831e91 /sha1_file.c
parente8964a5b91e13169ad73c7b1db2e904441ad93f5 (diff)
Don't smash stack when $GIT_ALTERNATE_OBJECT_DIRECTORIES is too long
There is no restriction on the length of the name returned by get_object_directory, other than the fact that it must be a stat'able git object directory. That means its name may have length up to PATH_MAX-1 (i.e., often 4095) not counting the trailing NUL. Combine that with the assumption that the concatenation of that name and suffixes like "/info/alternates" and "/pack/---long-name---.idx" will fit in a buffer of length PATH_MAX, and you see the problem. Here's a fix: sha1_file.c (prepare_packed_git_one): Lengthen "path" buffer so we are guaranteed to be able to append "/pack/" without checking. Skip any directory entry that is too long to be appended. (read_info_alternates): Protect against a similar buffer overrun. Before this change, using the following admittedly contrived environment setting would cause many git commands to clobber their stack and segfault on a system with PATH_MAX == 4096: t=$(perl -e '$s=".git/objects";$n=(4096-6-length($s))/2;print "./"x$n . $s') export GIT_ALTERNATE_OBJECT_DIRECTORIES=$t touch g ./git-update-index --add g If you run the above commands, you'll soon notice that many git commands now segfault, so you'll want to do this: unset GIT_ALTERNATE_OBJECT_DIRECTORIES Signed-off-by: Jim Meyering <> Signed-off-by: Junio C Hamano <>
Diffstat (limited to 'sha1_file.c')
1 files changed, 13 insertions, 3 deletions
diff --git a/sha1_file.c b/sha1_file.c
index b9d07de..1d328c8 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -352,10 +352,14 @@ static void read_info_alternates(const char * relative_base, int depth)
char *map;
size_t mapsz;
struct stat st;
- char path[PATH_MAX];
+ const char alt_file_name[] = "info/alternates";
+ /* Given that relative_base is no longer than PATH_MAX,
+ ensure that "path" has enough space to append "/", the
+ file name, "info/alternates", and a trailing NUL. */
+ char path[PATH_MAX + 1 + sizeof alt_file_name];
int fd;
- sprintf(path, "%s/info/alternates", relative_base);
+ sprintf(path, "%s/%s", relative_base, alt_file_name);
fd = open(path, O_RDONLY);
if (fd < 0)
@@ -814,7 +818,10 @@ void install_packed_git(struct packed_git *pack)
static void prepare_packed_git_one(char *objdir, int local)
- char path[PATH_MAX];
+ /* Ensure that this buffer is large enough so that we can
+ append "/pack/" without clobbering the stack even if
+ strlen(objdir) were PATH_MAX. */
+ char path[PATH_MAX + 1 + 4 + 1 + 1];
int len;
DIR *dir;
struct dirent *de;
@@ -836,6 +843,9 @@ static void prepare_packed_git_one(char *objdir, int local)
if (!has_extension(de->d_name, ".idx"))
+ if (len + namelen + 1 > sizeof(path))
+ continue;
/* Don't reopen a pack we already have. */
strcpy(path + len, de->d_name);
for (p = packed_git; p; p = p->next) {