memory leak in mpihelp_mul_karatsuba_case

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: abf02e29 Merge tag 'pm-5.2-rc6' of git://git.kernel.org/pu..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17a8bfeaa00000
kernel config: https://syzkaller.appspot.com/x/.config?x=56f1da14935c3cce
dashboard link: https://syzkaller.appspot.com/bug?extid=f7baccc38dcc1e094e77
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=171aa7e6a00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=153306cea00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f7bacc...@syzkaller.appspotmail.com

ffffffffda RBX: 0000000000000000 RCX: 0000000000441ac9
BUG: memory leak
unreferenced object 0xffff88811f4da200 (size 512):
comm "syz-executor301", pid 7045, jiffies 4294955450 (age 7.850s)
hex dump (first 32 bytes):
ad dc f4 43 66 b0 1a 88 8f 0c 17 d5 86 34 3a 85 ...Cf........4:.
e3 63 c8 bf 2e 3b f5 0d 1c ab 63 30 15 fe a1 e9 .c...;....c0....
backtrace:
[<00000000d5589961>] kmemleak_alloc_recursive
include/linux/kmemleak.h:43 [inline]
[<00000000d5589961>] slab_post_alloc_hook mm/slab.h:439 [inline]
[<00000000d5589961>] slab_alloc mm/slab.c:3326 [inline]
[<00000000d5589961>] __do_kmalloc mm/slab.c:3658 [inline]
[<00000000d5589961>] __kmalloc+0x161/0x2c0 mm/slab.c:3669
[<00000000022eaa00>] kmalloc include/linux/slab.h:552 [inline]
[<00000000022eaa00>] mpi_alloc_limb_space+0x29/0x50 lib/mpi/mpiutil.c:64
[<00000000d637c699>] mpihelp_mul_karatsuba_case+0x67/0x460
lib/mpi/mpih-mul.c:331
[<00000000401dc6f9>] mpi_powm+0x7b0/0xdd0 lib/mpi/mpi-pow.c:225
[<00000000be8dcb84>] _compute_val crypto/dh.c:39 [inline]
[<00000000be8dcb84>] dh_compute_value+0x160/0x220 crypto/dh.c:178
[<00000000471846ad>] crypto_kpp_generate_public_key
include/crypto/kpp.h:315 [inline]
[<00000000471846ad>] __keyctl_dh_compute+0x447/0x970
security/keys/dh.c:367
[<000000002f6d650d>] keyctl_dh_compute+0x67/0xa6 security/keys/dh.c:422
[<00000000b798bc7f>] __do_sys_keyctl security/keys/keyctl.c:1737
[inline]
[<00000000b798bc7f>] __se_sys_keyctl security/keys/keyctl.c:1633
[inline]
[<00000000b798bc7f>] __x64_sys_keyctl+0xa5/0x330
security/keys/keyctl.c:1633
[<000000007a6f9515>] do_syscall_64+0x76/0x1a0
arch/x86/entry/common.c:301
[<00000000057f2768>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

BUG: memory leak
unreferenced object 0xffff88811f4dac00 (size 512):
comm "syz-executor301", pid 7045, jiffies 4294955450 (age 7.850s)
hex dump (first 32 bytes):
62 72 c4 ae ac af a3 ba e5 24 da a5 30 5e cb c4 br.......$..0^..
a6 46 44 39 76 2e 42 f6 85 6a 5b ad ae 97 4e 83 .FD9v.B..j[...N.
backtrace:
[<00000000d5589961>] kmemleak_alloc_recursive
include/linux/kmemleak.h:43 [inline]
[<00000000d5589961>] slab_post_alloc_hook mm/slab.h:439 [inline]
[<00000000d5589961>] slab_alloc mm/slab.c:3326 [inline]
[<00000000d5589961>] __do_kmalloc mm/slab.c:3658 [inline]
[<00000000d5589961>] __kmalloc+0x161/0x2c0 mm/slab.c:3669
[<00000000022eaa00>] kmalloc include/linux/slab.h:552 [inline]
[<00000000022eaa00>] mpi_alloc_limb_space+0x29/0x50 lib/mpi/mpiutil.c:64
[<0000000025804541>] mpihelp_mul_karatsuba_case+0x394/0x460
lib/mpi/mpih-mul.c:346
[<00000000401dc6f9>] mpi_powm+0x7b0/0xdd0 lib/mpi/mpi-pow.c:225
[<00000000be8dcb84>] _compute_val crypto/dh.c:39 [inline]
[<00000000be8dcb84>] dh_compute_value+0x160/0x220 crypto/dh.c:178
[<00000000471846ad>] crypto_kpp_generate_public_key
include/crypto/kpp.h:315 [inline]
[<00000000471846ad>] __keyctl_dh_compute+0x447/0x970
security/keys/dh.c:367
[<000000002f6d650d>] keyctl_dh_compute+0x67/0xa6 security/keys/dh.c:422
[<00000000b798bc7f>] __do_sys_keyctl security/keys/keyctl.c:1737
[inline]
[<00000000b798bc7f>] __se_sys_keyctl security/keys/keyctl.c:1633
[inline]
[<00000000b798bc7f>] __x64_sys_keyctl+0xa5/0x330
security/keys/keyctl.c:1633
[<000000007a6f9515>] do_syscall_64+0x76/0x1a0
arch/x86/entry/common.c:301
[<00000000057f2768>] entry_SYSCALL_64_after_hwframe+0x44/0xa9



---
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[Herbert Xu]

On Mon, Jun 24, 2019 at 12:27:08AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: abf02e29 Merge tag 'pm-5.2-rc6' of git://git.kernel.org/pu..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17a8bfeaa00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=56f1da14935c3cce
> dashboard link: https://syzkaller.appspot.com/bug?extid=f7baccc38dcc1e094e77
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=171aa7e6a00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=153306cea00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+f7bacc...@syzkaller.appspotmail.com

The only memory leak that I can find is on the out-of-memory error
path:

---8<---
Sometimes mpi_powm will leak karactx because a memory allocation
failure causes a bail-out that skips the freeing of karactx. This
patch moves the freeing of karactx to the end of the function like
everything else so that it can't be skipped.

Reported-by: syzbot+f7bacc...@syzkaller.appspotmail.com
Fixes: cdec9cb5167a ("crypto: GnuPG based MPI lib - source files...")
Cc: <sta...@vger.kernel.org>
Signed-off-by: Herbert Xu <her...@gondor.apana.org.au>

diff --git a/lib/mpi/mpi-pow.c b/lib/mpi/mpi-pow.c
index 82b19e4f1189..2fd7a46d55ec 100644
--- a/lib/mpi/mpi-pow.c
+++ b/lib/mpi/mpi-pow.c
@@ -24,6 +24,7 @@
int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
{
mpi_ptr_t mp_marker = NULL, bp_marker = NULL, ep_marker = NULL;
+ struct karatsuba_ctx karactx = {};
mpi_ptr_t xp_marker = NULL;
mpi_ptr_t tspace = NULL;
mpi_ptr_t rp, ep, mp, bp;
@@ -150,13 +151,11 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
int c;
mpi_limb_t e;
mpi_limb_t carry_limb;
- struct karatsuba_ctx karactx;

xp = xp_marker = mpi_alloc_limb_space(2 * (msize + 1));
if (!xp)
goto enomem;

- memset(&karactx, 0, sizeof karactx);
negative_result = (ep[0] & 1) && base->sign;

i = esize - 1;
@@ -281,8 +280,6 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
if (mod_shift_cnt)
mpihelp_rshift(rp, rp, rsize, mod_shift_cnt);
MPN_NORMALIZE(rp, rsize);
-
- mpihelp_release_karatsuba_ctx(&karactx);
}

if (negative_result && rsize) {
@@ -299,6 +296,7 @@ int mpi_powm(MPI res, MPI base, MPI exp, MPI mod)
leave:
rc = 0;
enomem:
+ mpihelp_release_karatsuba_ctx(&karactx);
if (assign_rp)
mpi_assign_limb_space(res, rp, size);
if (mp_marker)
--
Email: Herbert Xu <her...@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

[Eric Biggers]

Reviewed-by: Eric Biggers <ebig...@kernel.org>

- Eric