linux-kernel - Re: [syzbot] [mm?] WARNING in try_grab

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Message-ID: <125377.1690360290@warthog.procyon.org.uk>
Date:   Wed, 26 Jul 2023 09:31:30 +0100
From:   David Howells <dhowells@...hat.com>
To:     syzbot <syzbot+9b82859567f2e50c123e@...kaller.appspotmail.com>
Cc:     dhowells@...hat.com, Sven Schnelle <svens@...ux.ibm.com>,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, syzkaller-bugs@...glegroups.com,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org
Subject: Re: [syzbot] [mm?] WARNING in try_grab_page

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

lib/scatterlist: Fix error handling in extract_iter_to_sg()

Fix the error handling in extract_iter_to_sg().  Pages need to be unpinned,
not put, and only if they actually got pinned (which is the case in
extract_user_to_sg()).

The bug may result in a warning like the following:

  WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:27 [inline]
  WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline]
  WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 raw_atomic_add include/linux/atomic/atomic-arch-fallback.h:537 [inline]
  WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 atomic_add include/linux/atomic/atomic-instrumented.h:105 [inline]
  WARNING: CPU: 1 PID: 20384 at mm/gup.c:229 try_grab_page+0x108/0x160 mm/gup.c:252
  ...
  pc : try_grab_page+0x108/0x160 mm/gup.c:229
  lr : follow_page_pte+0x174/0x3e4 mm/gup.c:651
  ...
  Call trace:
   __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:27 [inline]
   arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline]
   raw_atomic_add include/linux/atomic/atomic-arch-fallback.h:537 [inline]
   atomic_add include/linux/atomic/atomic-instrumented.h:105 [inline]
   try_grab_page+0x108/0x160 mm/gup.c:252
   follow_pmd_mask mm/gup.c:734 [inline]
   follow_pud_mask mm/gup.c:765 [inline]
   follow_p4d_mask mm/gup.c:782 [inline]
   follow_page_mask+0x12c/0x2e4 mm/gup.c:839
   __get_user_pages+0x174/0x30c mm/gup.c:1217
   __get_user_pages_locked mm/gup.c:1448 [inline]
   __gup_longterm_locked+0x94/0x8f4 mm/gup.c:2142
   internal_get_user_pages_fast+0x970/0xb60 mm/gup.c:3140
   pin_user_pages_fast+0x4c/0x60 mm/gup.c:3246
   iov_iter_extract_user_pages lib/iov_iter.c:1768 [inline]
   iov_iter_extract_pages+0xc8/0x54c lib/iov_iter.c:1831
   extract_user_to_sg lib/scatterlist.c:1123 [inline]
   extract_iter_to_sg lib/scatterlist.c:1349 [inline]
   extract_iter_to_sg+0x26c/0x6fc lib/scatterlist.c:1339
   hash_sendmsg+0xc0/0x43c crypto/algif_hash.c:117
   sock_sendmsg_nosec net/socket.c:725 [inline]
   sock_sendmsg+0x54/0x60 net/socket.c:748
   ____sys_sendmsg+0x270/0x2ac net/socket.c:2494
   ___sys_sendmsg+0x80/0xdc net/socket.c:2548
   __sys_sendmsg+0x68/0xc4 net/socket.c:2577
   __do_sys_sendmsg net/socket.c:2586 [inline]
   __se_sys_sendmsg net/socket.c:2584 [inline]
   __arm64_sys_sendmsg+0x24/0x30 net/socket.c:2584
   __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
   invoke_syscall+0x48/0x114 arch/arm64/kernel/syscall.c:52
   el0_svc_common.constprop.0+0x44/0xe4 arch/arm64/kernel/syscall.c:142
   do_el0_svc+0x38/0xa4 arch/arm64/kernel/syscall.c:191
   el0_svc+0x2c/0xb0 arch/arm64/kernel/entry-common.c:647
   el0t_64_sync_handler+0xc0/0xc4 arch/arm64/kernel/entry-common.c:665
   el0t_64_sync+0x19c/0x1a0 arch/arm64/kernel/entry.S:591

Fixes: 018584697533 ("netfs: Add a function to extract an iterator into a scatterlist")
Reported-by: syzbot+9b82859567f2e50c123e@...kaller.appspotmail.com
Link: https://lore.kernel.org/linux-mm/000000000000273d0105ff97bf56@google.com/
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Sven Schnelle <svens@...ux.ibm.com>
cc: akpm@...ux-foundation.org
cc: Herbert Xu <herbert@...dor.apana.org.au>
cc: "David S. Miller" <davem@...emloft.net>
cc: Jeff Layton <jlayton@...nel.org>
cc: Steve French <sfrench@...ba.org>
cc: Shyam Prasad N <nspmangalore@...il.com>
cc: Rohith Surabattula <rohiths.msft@...il.com>
cc: Jens Axboe <axboe@...nel.dk>
cc: Herbert Xu <herbert@...dor.apana.org.au>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: Matthew Wilcox <willy@...radead.org>
cc: linux-mm@...ck.org
cc: linux-crypto@...r.kernel.org
cc: linux-cachefs@...hat.com
cc: linux-cifs@...r.kernel.org
cc: linux-fsdevel@...r.kernel.org
cc: netdev@...r.kernel.org
---
 lib/scatterlist.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index e86231a44c3d..c65566b4dc66 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -1148,7 +1148,7 @@ static ssize_t extract_user_to_sg(struct iov_iter *iter,
 
 failed:
 	while (sgtable->nents > sgtable->orig_nents)
-		put_page(sg_page(&sgtable->sgl[--sgtable->nents]));
+		unpin_user_page(sg_page(&sgtable->sgl[--sgtable->nents]));
 	return res;
 }