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authorVegard Nossum <vegard.nossum@oracle.com>2016-07-29 10:40:31 +0200
committerJens Axboe <axboe@fb.com>2016-08-04 14:19:16 -0600
commit77da160530dd1dc94f6ae15a981f24e5f0021e84 (patch)
tree9eec0224d03d5de61f635f6cceb2fc62ffda64d7
parent1aee6b9a7d947d42ed84baa4cf461e9d943b80f0 (diff)
block: fix use-after-free in seq file
I got a KASAN report of use-after-free: ================================================================== BUG: KASAN: use-after-free in klist_iter_exit+0x61/0x70 at addr ffff8800b6581508 Read of size 8 by task trinity-c1/315 ============================================================================= BUG kmalloc-32 (Not tainted): kasan: bad access detected ----------------------------------------------------------------------------- Disabling lock debugging due to kernel taint INFO: Allocated in disk_seqf_start+0x66/0x110 age=144 cpu=1 pid=315 ___slab_alloc+0x4f1/0x520 __slab_alloc.isra.58+0x56/0x80 kmem_cache_alloc_trace+0x260/0x2a0 disk_seqf_start+0x66/0x110 traverse+0x176/0x860 seq_read+0x7e3/0x11a0 proc_reg_read+0xbc/0x180 do_loop_readv_writev+0x134/0x210 do_readv_writev+0x565/0x660 vfs_readv+0x67/0xa0 do_preadv+0x126/0x170 SyS_preadv+0xc/0x10 do_syscall_64+0x1a1/0x460 return_from_SYSCALL_64+0x0/0x6a INFO: Freed in disk_seqf_stop+0x42/0x50 age=160 cpu=1 pid=315 __slab_free+0x17a/0x2c0 kfree+0x20a/0x220 disk_seqf_stop+0x42/0x50 traverse+0x3b5/0x860 seq_read+0x7e3/0x11a0 proc_reg_read+0xbc/0x180 do_loop_readv_writev+0x134/0x210 do_readv_writev+0x565/0x660 vfs_readv+0x67/0xa0 do_preadv+0x126/0x170 SyS_preadv+0xc/0x10 do_syscall_64+0x1a1/0x460 return_from_SYSCALL_64+0x0/0x6a CPU: 1 PID: 315 Comm: trinity-c1 Tainted: G B 4.7.0+ #62 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 ffffea0002d96000 ffff880119b9f918 ffffffff81d6ce81 ffff88011a804480 ffff8800b6581500 ffff880119b9f948 ffffffff8146c7bd ffff88011a804480 ffffea0002d96000 ffff8800b6581500 fffffffffffffff4 ffff880119b9f970 Call Trace: [<ffffffff81d6ce81>] dump_stack+0x65/0x84 [<ffffffff8146c7bd>] print_trailer+0x10d/0x1a0 [<ffffffff814704ff>] object_err+0x2f/0x40 [<ffffffff814754d1>] kasan_report_error+0x221/0x520 [<ffffffff8147590e>] __asan_report_load8_noabort+0x3e/0x40 [<ffffffff83888161>] klist_iter_exit+0x61/0x70 [<ffffffff82404389>] class_dev_iter_exit+0x9/0x10 [<ffffffff81d2e8ea>] disk_seqf_stop+0x3a/0x50 [<ffffffff8151f812>] seq_read+0x4b2/0x11a0 [<ffffffff815f8fdc>] proc_reg_read+0xbc/0x180 [<ffffffff814b24e4>] do_loop_readv_writev+0x134/0x210 [<ffffffff814b4c45>] do_readv_writev+0x565/0x660 [<ffffffff814b8a17>] vfs_readv+0x67/0xa0 [<ffffffff814b8de6>] do_preadv+0x126/0x170 [<ffffffff814b92ec>] SyS_preadv+0xc/0x10 This problem can occur in the following situation: open() - pread() - .seq_start() - iter = kmalloc() // succeeds - seqf->private = iter - .seq_stop() - kfree(seqf->private) - pread() - .seq_start() - iter = kmalloc() // fails - .seq_stop() - class_dev_iter_exit(seqf->private) // boom! old pointer As the comment in disk_seqf_stop() says, stop is called even if start failed, so we need to reinitialise the private pointer to NULL when seq iteration stops. An alternative would be to set the private pointer to NULL when the kmalloc() in disk_seqf_start() fails. Cc: stable@vger.kernel.org Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Jens Axboe <axboe@fb.com>
-rw-r--r--block/genhd.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/block/genhd.c b/block/genhd.c
index 3c9dede..0ad8796 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -856,6 +856,7 @@ static void disk_seqf_stop(struct seq_file *seqf, void *v)
if (iter) {
class_dev_iter_exit(iter);
kfree(iter);
+ seqf->private = NULL;
}
}