undef/git-commit-vandalism
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Don't smash stack when $GIT_ALTERNATE_OBJECT_DIRECTORIES is too long

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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 <jim@meyering.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jim Meyering 2007-07-03 12:40:20 +02:00 committed by Junio C Hamano
parent e8964a5b91
commit 9cb18f56fd
1 changed files with 13 additions and 3 deletions
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16
sha1_file.c
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@ -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)
return;
@ -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"))
continue;
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) {