Subject: + coredump-set_dumpable-fix-the-theoretical-race-with-itself.patch added to -mm tree
To: oleg@xxxxxxxxxx,alex.page.kelly@xxxxxxxxx,ebiederm@xxxxxxxxxxxx,josh@xxxxxxxxxxxxxxxx,keescook@xxxxxxxxxxxx,pmatouse@xxxxxxxxxx,segoon@xxxxxxxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Tue, 19 Nov 2013 14:22:12 -0800
The patch titled
Subject: coredump: set_dumpable: fix the theoretical race with itself
has been added to the -mm tree. Its filename is
coredump-set_dumpable-fix-the-theoretical-race-with-itself.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/coredump-set_dumpable-fix-the-theoretical-race-with-itself.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/coredump-set_dumpable-fix-the-theoretical-race-with-itself.patch
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: coredump: set_dumpable: fix the theoretical race with itself
set_dumpable() updates MMF_DUMPABLE_MASK in a non-trivial way to ensure
that get_dumpable() can't observe the intermediate state, but this all
can't help if multiple threads call set_dumpable() at the same time.
And in theory commit_creds()->set_dumpable(SUID_DUMP_ROOT) racing with
sys_prctl()->set_dumpable(SUID_DUMP_DISABLE) can result in SUID_DUMP_USER.
Change this code to update both bits atomically via cmpxchg().
Note: this assumes that it is safe to mix bitops and cmpxchg. IOW, if,
say, an architecture implements cmpxchg() using the locking (like
arch/parisc/lib/bitops.c does), then it should use the same locks for
set_bit/etc.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Alex Kelly <alex.page.kelly@xxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Petr Matousek <pmatouse@xxxxxxxxxx>
Cc: Vasily Kulikov <segoon@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/exec.c | 49 +++++++++++++++----------------------------------
1 file changed, 15 insertions(+), 34 deletions(-)
diff -puN fs/exec.c~coredump-set_dumpable-fix-the-theoretical-race-with-itself fs/exec.c
--- a/fs/exec.c~coredump-set_dumpable-fix-the-theoretical-race-with-itself
+++ a/fs/exec.c
@@ -1617,43 +1617,24 @@ EXPORT_SYMBOL(set_binfmt);
/*
* set_dumpable converts traditional three-value dumpable to two flags and
- * stores them into mm->flags. It modifies lower two bits of mm->flags, but
- * these bits are not changed atomically. So get_dumpable can observe the
- * intermediate state. To avoid doing unexpected behavior, get get_dumpable
- * return either old dumpable or new one by paying attention to the order of
- * modifying the bits.
- *
- * dumpable | mm->flags (binary)
- * old new | initial interim final
- * ---------+-----------------------
- * 0 1 | 00 01 01
- * 0 2 | 00 10(*) 11
- * 1 0 | 01 00 00
- * 1 2 | 01 11 11
- * 2 0 | 11 10(*) 00
- * 2 1 | 11 11 01
- *
- * (*) get_dumpable regards interim value of 10 as 11.
+ * stores them into mm->flags.
*/
void set_dumpable(struct mm_struct *mm, int value)
{
- switch (value) {
- case SUID_DUMP_DISABLE:
- clear_bit(MMF_DUMPABLE, &mm->flags);
- smp_wmb();
- clear_bit(MMF_DUMP_SECURELY, &mm->flags);
- break;
- case SUID_DUMP_USER:
- set_bit(MMF_DUMPABLE, &mm->flags);
- smp_wmb();
- clear_bit(MMF_DUMP_SECURELY, &mm->flags);
- break;
- case SUID_DUMP_ROOT:
- set_bit(MMF_DUMP_SECURELY, &mm->flags);
- smp_wmb();
- set_bit(MMF_DUMPABLE, &mm->flags);
- break;
- }
+ unsigned long old, new;
+
+ do {
+ old = ACCESS_ONCE(mm->flags);
+ new = old & ~MMF_DUMPABLE_MASK;
+
+ switch (value) {
+ case SUID_DUMP_ROOT:
+ new |= (1 << MMF_DUMP_SECURELY);
+ case SUID_DUMP_USER:
+ new |= (1<< MMF_DUMPABLE);
+ }
+
+ } while (cmpxchg(&mm->flags, old, new) != old);
}
int __get_dumpable(unsigned long mm_flags)
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
origin.patch
autofs4-allow-autofs-to-work-outside-the-initial-pid-namespace.patch
autofs4-translate-pids-to-the-right-namespace-for-the-daemon.patch
coredump-set_dumpable-fix-the-theoretical-race-with-itself.patch
coredump-kill-mmf_dumpable-and-mmf_dump_securely.patch
coredump-make-__get_dumpable-get_dumpable-inline-kill-fs-coredumph.patch
linux-next.patch
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