134 lines
4.1 KiB
Diff
134 lines
4.1 KiB
Diff
From: Kees Cook <keescook@chromium.org>
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Date: Thu, 6 Dec 2012 17:00:21 +1100
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Subject: [2/2] exec: use -ELOOP for max recursion depth
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commit a4706fd3dc5d23f58da814d03f3ef92fd9a4fc16 upstream.
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To avoid an explosion of request_module calls on a chain of abusive
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scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon
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as maximum recursion depth is hit, the error will fail all the way back
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up the chain, aborting immediately.
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This also has the side-effect of stopping the user's shell from attempting
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to reexecute the top-level file as a shell script. As seen in the
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dash source:
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if (cmd != path_bshell && errno == ENOEXEC) {
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*argv-- = cmd;
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*argv = cmd = path_bshell;
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goto repeat;
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}
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The above logic was designed for running scripts automatically that lacked
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the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC,
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things continue to behave as the shell expects.
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Additionally, when tracking recursion, the binfmt handlers should not be
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involved. The recursion being tracked is the depth of calls through
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search_binary_handler(), so that function should be exclusively responsible
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for tracking the depth.
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Signed-off-by: Kees Cook <keescook@chromium.org>
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Cc: halfdog <me@halfdog.net>
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Cc: P J P <ppandit@redhat.com>
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Cc: Alexander Viro <viro@zeniv.linux.org.uk>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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[bwh: Backported to 3.6: adjust context]
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---
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fs/binfmt_em86.c | 1 -
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fs/binfmt_misc.c | 6 ------
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fs/binfmt_script.c | 4 +---
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fs/exec.c | 10 +++++-----
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include/linux/binfmts.h | 2 --
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5 files changed, 6 insertions(+), 17 deletions(-)
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--- a/fs/binfmt_em86.c
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+++ b/fs/binfmt_em86.c
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@@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm
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return -ENOEXEC;
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}
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- bprm->recursion_depth++; /* Well, the bang-shell is implicit... */
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allow_write_access(bprm->file);
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fput(bprm->file);
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bprm->file = NULL;
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--- a/fs/binfmt_misc.c
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+++ b/fs/binfmt_misc.c
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@@ -117,10 +117,6 @@ static int load_misc_binary(struct linux
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if (!enabled)
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goto _ret;
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- retval = -ENOEXEC;
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- if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
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- goto _ret;
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-
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/* to keep locking time low, we copy the interpreter string */
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read_lock(&entries_lock);
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fmt = check_file(bprm);
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@@ -200,8 +196,6 @@ static int load_misc_binary(struct linux
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if (retval < 0)
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goto _error;
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- bprm->recursion_depth++;
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-
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retval = search_binary_handler (bprm, regs);
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if (retval < 0)
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goto _error;
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--- a/fs/binfmt_script.c
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+++ b/fs/binfmt_script.c
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@@ -22,15 +22,13 @@ static int load_script(struct linux_binp
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char interp[BINPRM_BUF_SIZE];
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int retval;
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- if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') ||
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- (bprm->recursion_depth > BINPRM_MAX_RECURSION))
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+ if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
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return -ENOEXEC;
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/*
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* This section does the #! interpretation.
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* Sorta complicated, but hopefully it will work. -TYT
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*/
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- bprm->recursion_depth++;
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allow_write_access(bprm->file);
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fput(bprm->file);
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bprm->file = NULL;
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--- a/fs/exec.c
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+++ b/fs/exec.c
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@@ -1371,6 +1371,10 @@ int search_binary_handler(struct linux_b
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struct linux_binfmt *fmt;
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pid_t old_pid, old_vpid;
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+ /* This allows 4 levels of binfmt rewrites before failing hard. */
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+ if (depth > 5)
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+ return -ELOOP;
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+
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retval = security_bprm_check(bprm);
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if (retval)
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return retval;
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@@ -1395,12 +1399,8 @@ int search_binary_handler(struct linux_b
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if (!try_module_get(fmt->module))
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continue;
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read_unlock(&binfmt_lock);
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+ bprm->recursion_depth = depth + 1;
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retval = fn(bprm, regs);
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- /*
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- * Restore the depth counter to its starting value
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- * in this call, so we don't have to rely on every
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- * load_binary function to restore it on return.
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- */
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bprm->recursion_depth = depth;
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if (retval >= 0) {
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if (depth == 0) {
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--- a/include/linux/binfmts.h
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+++ b/include/linux/binfmts.h
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@@ -54,8 +54,6 @@ struct linux_binprm {
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#define BINPRM_FLAGS_EXECFD_BIT 1
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#define BINPRM_FLAGS_EXECFD (1 << BINPRM_FLAGS_EXECFD_BIT)
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-#define BINPRM_MAX_RECURSION 4
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-
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/* Function parameter for binfmt->coredump */
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struct coredump_params {
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siginfo_t *siginfo;
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