From 023eae6de094c527f85c5fc3e9a8a364af56b1af Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 17 Dec 2012 16:03:20 -0800 Subject: [PATCH] exec: use -ELOOP for max recursion depth commit d740269867021faf4ce38a449353d2b986c34a67 upstream. 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 Cc: halfdog Cc: P J P Cc: Alexander Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Cc: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- fs/binfmt_em86.c | 1 - fs/binfmt_misc.c | 6 ------ fs/binfmt_script.c | 4 +--- fs/exec.c | 10 +++++----- include/linux/binfmts.h | 2 -- 5 files changed, 6 insertions(+), 17 deletions(-) diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c index 2790c7e1912e..575796ae3d84 100644 --- a/fs/binfmt_em86.c +++ b/fs/binfmt_em86.c @@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm *bprm,struct pt_regs *regs) 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 e1724392d050..87fa90d5863b 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -117,10 +117,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs) 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); @@ -200,8 +196,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs) if (retval < 0) goto _error; - bprm->recursion_depth++; - retval = search_binary_handler (bprm, regs); if (retval < 0) goto _error; diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c index df49d486b0c0..8ae4be199fb4 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -22,15 +22,13 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs) 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; diff --git a/fs/exec.c b/fs/exec.c index 51d862973639..e3a7e36dcd44 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1389,6 +1389,10 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs) 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; @@ -1413,12 +1417,8 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs) if (!try_module_get(fmt->module)) continue; read_unlock(&binfmt_lock); + bprm->recursion_depth = depth + 1; retval = fn(bprm, regs); - /* - * 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) { diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index eb53e15ede68..5bab59b1034e 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -68,8 +68,6 @@ struct linux_binprm { #define BINPRM_FLAGS_EXECFD_BIT 1 #define BINPRM_FLAGS_EXECFD (1 << BINPRM_FLAGS_EXECFD_BIT) -#define BINPRM_MAX_RECURSION 4 - /* Function parameter for binfmt->coredump */ struct coredump_params { long signr;