diff options
author | Kees Cook <keescook@chromium.org> | 2012-12-17 16:03:20 -0800 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-12-17 17:15:23 -0800 |
commit | d740269867021faf4ce38a449353d2b986c34a67 (patch) | |
tree | e0476e1be1dfb6e852adbaa8fb72ecea87bdb088 /fs | |
parent | 8d238027b87e654be552eabdf492042a34c5c300 (diff) | |
download | op-kernel-dev-d740269867021faf4ce38a449353d2b986c34a67.zip op-kernel-dev-d740269867021faf4ce38a449353d2b986c34a67.tar.gz |
exec: use -ELOOP for max recursion depth
To avoid an explosion of request_module calls on a chain of abusive
scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon
as maximum recursion depth is hit, the error will fail all the way back
up the chain, aborting immediately.
This also has the side-effect of stopping the user's shell from attempting
to reexecute the top-level file as a shell script. As seen in the
dash source:
if (cmd != path_bshell && errno == ENOEXEC) {
*argv-- = cmd;
*argv = cmd = path_bshell;
goto repeat;
}
The above logic was designed for running scripts automatically that lacked
the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC,
things continue to behave as the shell expects.
Additionally, when tracking recursion, the binfmt handlers should not be
involved. The recursion being tracked is the depth of calls through
search_binary_handler(), so that function should be exclusively responsible
for tracking the depth.
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: halfdog <me@halfdog.net>
Cc: P J P <ppandit@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/binfmt_em86.c | 1 | ||||
-rw-r--r-- | fs/binfmt_misc.c | 6 | ||||
-rw-r--r-- | fs/binfmt_script.c | 4 | ||||
-rw-r--r-- | fs/exec.c | 10 |
4 files changed, 6 insertions, 15 deletions
diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c index 4e6cce5..037a3e2 100644 --- a/fs/binfmt_em86.c +++ b/fs/binfmt_em86.c @@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm *bprm) return -ENOEXEC; } - bprm->recursion_depth++; /* Well, the bang-shell is implicit... */ allow_write_access(bprm->file); fput(bprm->file); bprm->file = NULL; diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index b0b70fb..9be335f 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -117,10 +117,6 @@ static int load_misc_binary(struct linux_binprm *bprm) if (!enabled) goto _ret; - retval = -ENOEXEC; - if (bprm->recursion_depth > BINPRM_MAX_RECURSION) - goto _ret; - /* to keep locking time low, we copy the interpreter string */ read_lock(&entries_lock); fmt = check_file(bprm); @@ -197,8 +193,6 @@ static int load_misc_binary(struct linux_binprm *bprm) if (retval < 0) goto _error; - bprm->recursion_depth++; - retval = search_binary_handler(bprm); if (retval < 0) goto _error; diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c index 8c95499..1610a91 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -22,15 +22,13 @@ static int load_script(struct linux_binprm *bprm) char interp[BINPRM_BUF_SIZE]; int retval; - if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') || - (bprm->recursion_depth > BINPRM_MAX_RECURSION)) + if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!')) return -ENOEXEC; /* * This section does the #! interpretation. * Sorta complicated, but hopefully it will work. -TYT */ - bprm->recursion_depth++; allow_write_access(bprm->file); fput(bprm->file); bprm->file = NULL; @@ -1356,6 +1356,10 @@ int search_binary_handler(struct linux_binprm *bprm) struct linux_binfmt *fmt; pid_t old_pid, old_vpid; + /* This allows 4 levels of binfmt rewrites before failing hard. */ + if (depth > 5) + return -ELOOP; + retval = security_bprm_check(bprm); if (retval) return retval; @@ -1380,12 +1384,8 @@ int search_binary_handler(struct linux_binprm *bprm) if (!try_module_get(fmt->module)) continue; read_unlock(&binfmt_lock); + bprm->recursion_depth = depth + 1; retval = fn(bprm); - /* - * Restore the depth counter to its starting value - * in this call, so we don't have to rely on every - * load_binary function to restore it on return. - */ bprm->recursion_depth = depth; if (retval >= 0) { if (depth == 0) { |