Messages in this thread | | | From | Ard Biesheuvel <> | Date | Wed, 30 Jun 2021 09:42:14 +0200 | Subject | Re: [syzbot] BUG: sleeping function called from invalid context in __fdget_pos |
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On Tue, 29 Jun 2021 at 16:46, Dave Hansen <dave.hansen@intel.com> wrote: > > ... adding Ard who was recently modifying some of the > kernel_fpu_begin/end() sites in the AESNI crypto code. > > On 6/28/21 12:22 PM, syzbot wrote: > > console output: https://syzkaller.appspot.com/x/log.txt?x=170e6c94300000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=42ecca11b759d96c > > dashboard link: https://syzkaller.appspot.com/bug?extid=5d1bad8042a8f0e8117a > > > > Unfortunately, I don't have any reproducer for this issue yet. > ... > > BUG: sleeping function called from invalid context at kernel/locking/mutex.c:938 > > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 29652, name: syz-executor.0 > > no locks held by syz-executor.0/29652. > > Preemption disabled at: > > [<ffffffff812aa454>] kernel_fpu_begin_mask+0x64/0x260 arch/x86/kernel/fpu/core.c:126 > > CPU: 0 PID: 29652 Comm: syz-executor.0 Not tainted 5.13.0-rc7-syzkaller #0 > > There's a better backtrace in the log before the rather useless > backtrace from lockdep: > > > [ 1341.360547][T29635] FAULT_INJECTION: forcing a failure. > > [ 1341.360547][T29635] name failslab, interval 1, probability 0, space 0, times 0 > > [ 1341.374439][T29635] CPU: 1 PID: 29635 Comm: syz-executor.0 Not tainted 5.13.0-rc7-syzkaller #0 > > [ 1341.374712][T29630] FAT-fs (loop2): bogus number of reserved sectors > > [ 1341.383571][T29635] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > [ 1341.383591][T29635] Call Trace: > > [ 1341.383603][T29635] dump_stack+0x141/0x1d7 > > [ 1341.383630][T29635] should_fail.cold+0x5/0xa > > [ 1341.383651][T29635] ? skcipher_walk_next+0x6e2/0x1680 > > [ 1341.383673][T29635] should_failslab+0x5/0x10 > > [ 1341.383691][T29635] __kmalloc+0x72/0x330 > > [ 1341.383720][T29635] skcipher_walk_next+0x6e2/0x1680 > > [ 1341.383744][T29635] ? kfree+0xe5/0x7f0 > > [ 1341.383776][T29635] skcipher_walk_first+0xf8/0x3c0 > > [ 1341.383805][T29635] skcipher_walk_virt+0x523/0x760 > > [ 1341.445438][T29635] xts_crypt+0x137/0x7f0 > > [ 1341.449689][T29635] ? aesni_encrypt+0x80/0x80 > > There's one suspect-looking site in xts_crypt(): > > > kernel_fpu_begin(); > > > > /* calculate first value of T */ > > aesni_enc(aes_ctx(ctx->raw_tweak_ctx), walk.iv, walk.iv); > > > > while (walk.nbytes > 0) { > > int nbytes = walk.nbytes; > > > > ... > > > > err = skcipher_walk_done(&walk, walk.nbytes - nbytes); > > > > kernel_fpu_end(); > > > > if (walk.nbytes > 0) > > kernel_fpu_begin(); > > } > > I wonder if a slab allocation failure could leave us with walk.nbytes==0.
The code is actually the other way around: kernel_fpu_end() comes before the call to skcipher_walk_done().
So IIUC, this code forces an allocation failure, and checks whether the code deals with this gracefully, right?
The skcipher walk API guarantees that walk.nbytes == 0 if an error is returned, so the pairing of FPU begin/end looks correct to me. And skcipher_walk_next() should not invoke anything that might sleep from this particular context.
Herbert, any ideas?
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