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Subject[PATCH] Reset current->pdeath_signal on SUID binary execution
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Hi Linus,

the attached patch fixes a flaw in the "parent process death signal"
when executing SUID binaries. An unprivileged user may send arbitrary
signal to a child process even if it is running with higher privileges.

The idea to fix this issue is to reset pdeath_signal not only on fork,
but also on the execution of a SUID binary.

Michael, if we fix it this way, then the prctl() manual page should
reflect that behavior.

>From comments it seems that we have to also reset pdeath_signal inside
LSM when it comes to capability-raised executes, but I must admit that I
got lost there.

Regards

Marcel

[PATCH] Reset current->pdeath_signal on SUID binary execution

This fixes a vulnerability in the "parent process death signal"
implementation discoverd by Wojciech Purczynski of COSEINC PTE Ltd.
and iSEC Security Research.

http://marc.info/?l=bugtraq&m=118711306802632&w=2

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

---
commit 8542f23e44f591480ca53d215481cbec43b8cbed
tree d72f29856adb306f20e828d4bab244685fe24bf2
parent 6adb31c90c47262c8a25bf5097de9b3426caf3ae
author Marcel Holtmann <marcel@holtmann.org> Fri, 17 Aug 2007 21:41:52 +0200
committer Marcel Holtmann <marcel@holtmann.org> Fri, 17 Aug 2007 21:41:52 +0200
fs/exec.c | 13 +++++++++----
1 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 7bdea79..ce62f7b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1084,9 +1084,12 @@ int flush_old_exec(struct linux_binprm * bprm)
*/
current->mm->task_size = TASK_SIZE;

- if (bprm->e_uid != current->euid || bprm->e_gid != current->egid ||
- file_permission(bprm->file, MAY_READ) ||
- (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)) {
+ if (bprm->e_uid != current->euid || bprm->e_gid != current->egid) {
+ suid_keys(current);
+ set_dumpable(current->mm, suid_dumpable);
+ current->pdeath_signal = 0;
+ } else if (file_permission(bprm->file, MAY_READ) ||
+ (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)) {
suid_keys(current);
set_dumpable(current->mm, suid_dumpable);
}
@@ -1177,8 +1180,10 @@ void compute_creds(struct linux_binprm *bprm)
{
int unsafe;

- if (bprm->e_uid != current->uid)
+ if (bprm->e_uid != current->uid) {
suid_keys(current);
+ current->pdeath_signal = 0;
+ }
exec_keys(current);

task_lock(current);
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