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authorKees Cook <keescook@chromium.org>2012-12-18 04:03:20 +0400
committerLinus Torvalds <torvalds@linux-foundation.org>2012-12-18 05:15:23 +0400
commitd740269867021faf4ce38a449353d2b986c34a67 (patch)
treee0476e1be1dfb6e852adbaa8fb72ecea87bdb088 /fs/exec.c
parent8d238027b87e654be552eabdf492042a34c5c300 (diff)
downloadlinux-d740269867021faf4ce38a449353d2b986c34a67.tar.xz
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/exec.c')
-rw-r--r--fs/exec.c10
1 files changed, 5 insertions, 5 deletions
diff --git a/fs/exec.c b/fs/exec.c
index 721a29929511..d5eb9e605ffd 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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) {