[PATCH v6.13 v2] fs/netfs/read_collect: fix crash due to uninitialized `prev` variable

[PATCH v6.13 v2] fs/netfs/read_collect: fix crash due to uninitialized `prev` variable

[Max Kellermann]

When checking whether the edges of adjacent subrequests touch, the
`prev` variable is deferenced, but it might not have been initialized.
This causes crashes like this one:

 BUG: unable to handle page fault for address: 0000000181343843
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 8000001c66db0067 P4D 8000001c66db0067 PUD 0
 Oops: Oops: 0000 [#1] SMP PTI
 CPU: 1 UID: 33333 PID: 24424 Comm: php-cgi8.2 Kdump: loaded Not tainted 6.13.2-cm4all0-hp+ #427
 Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 11/23/2021
 RIP: 0010:netfs_consume_read_data.isra.0+0x5ef/0xb00
 Code: fe ff ff 48 8b 83 88 00 00 00 48 8b 4c 24 30 4c 8b 43 78 48 85 c0 48 8d 51 70 75 20 48 8b 73 30 48 39 d6 74 17 48 8b 7c 24 40 <48> 8b 4f 78 48 03 4f 68 48 39 4b 68 0f 84 ab 02 00 00 49 29 c0 48
 RSP: 0000:ffffc90037adbd00 EFLAGS: 00010283
 RAX: 0000000000000000 RBX: ffff88811bda0600 RCX: ffff888620e7b980
 RDX: ffff888620e7b9f0 RSI: ffff88811bda0428 RDI: 00000001813437cb
 RBP: 0000000000000000 R08: 0000000000004000 R09: 0000000000000000
 R10: ffffffff82e070c0 R11: 0000000007ffffff R12: 0000000000004000
 R13: ffff888620e7bb68 R14: 0000000000008000 R15: ffff888620e7bb68
 FS:  00007ff2e0e7ddc0(0000) GS:ffff88981f840000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000181343843 CR3: 0000001bc10ba006 CR4: 00000000001706f0
 Call Trace:
  <TASK>
  ? __die+0x1f/0x60
  ? page_fault_oops+0x15c/0x450
  ? search_extable+0x22/0x30
  ? netfs_consume_read_data.isra.0+0x5ef/0xb00
  ? search_module_extables+0xe/0x40
  ? exc_page_fault+0x5e/0x100
  ? asm_exc_page_fault+0x22/0x30
  ? netfs_consume_read_data.isra.0+0x5ef/0xb00
  ? intel_iommu_unmap_pages+0xaa/0x190
  ? __pfx_cachefiles_read_complete+0x10/0x10
  netfs_read_subreq_terminated+0x24f/0x390
  cachefiles_read_complete+0x48/0xf0
  iomap_dio_bio_end_io+0x125/0x160
  blk_update_request+0xea/0x3e0
  scsi_end_request+0x27/0x190
  scsi_io_completion+0x43/0x6c0
  blk_complete_reqs+0x40/0x50
  handle_softirqs+0xd1/0x280
  irq_exit_rcu+0x91/0xb0
  common_interrupt+0x3b/0xa0
  asm_common_interrupt+0x22/0x40
 RIP: 0033:0x55fe8470d2ab
 Code: 00 00 3c 7e 74 3b 3c b6 0f 84 dd 03 00 00 3c 1e 74 2f 83 c1 01 48 83 c2 38 48 83 c7 30 44 39 d1 74 3e 48 63 42 08 85 c0 79 a3 <49> 8b 46 48 8b 04 38 f6 c4 04 75 0b 0f b6 42 30 83 e0 0c 3c 04 75
 RSP: 002b:00007ffca5ef2720 EFLAGS: 00000216
 RAX: 0000000000000023 RBX: 0000000000000008 RCX: 000000000000001b
 RDX: 00007ff2e0cdb6f8 RSI: 0000000000000006 RDI: 0000000000000510
 RBP: 00007ffca5ef27a0 R08: 00007ffca5ef2720 R09: 0000000000000001
 R10: 000000000000001e R11: 00007ff2e0c10d08 R12: 0000000000000001
 R13: 0000000000000120 R14: 00007ff2e0cb1ed0 R15: 00000000000000b0
  </TASK>

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
---
David/Greg: just like the other two netfs patches I sent yesterday,
this one doesn't apply to v6.14 as it was obsoleted by commit
e2d46f2ec332 ("netfs: Change the read result collector to only use one
work item").

v1->v2: duplicate "prev" assigment removed.

Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
---
 fs/netfs/read_collect.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
index e8624f5c7fcc..8878b46589ff 100644
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -258,17 +258,18 @@ static bool netfs_consume_read_data(struct netfs_io_subrequest *subreq, bool was
 	 */
 	if (!subreq->consumed &&
 	    !prev_donated &&
-	    !list_is_first(&subreq->rreq_link, &rreq->subrequests) &&
-	    subreq->start == prev->start + prev->len) {
+	    !list_is_first(&subreq->rreq_link, &rreq->subrequests)) {
 		prev = list_prev_entry(subreq, rreq_link);
-		WRITE_ONCE(prev->next_donated, prev->next_donated + subreq->len);
-		subreq->start += subreq->len;
-		subreq->len = 0;
-		subreq->transferred = 0;
-		trace_netfs_donate(rreq, subreq, prev, subreq->len,
-				   netfs_trace_donate_to_prev);
-		trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
-		goto remove_subreq_locked;
+		if (subreq->start == prev->start + prev->len) {
+			WRITE_ONCE(prev->next_donated, prev->next_donated + subreq->len);
+			subreq->start += subreq->len;
+			subreq->len = 0;
+			subreq->transferred = 0;
+			trace_netfs_donate(rreq, subreq, prev, subreq->len,
+					   netfs_trace_donate_to_prev);
+			trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
+			goto remove_subreq_locked;
+		}
 	}
 
 	/* If we can't donate down the chain, donate up the chain instead. */
-- 
2.47.2

Re: [PATCH v6.13 v2] fs/netfs/read_collect: fix crash due to uninitialized `prev` variable

[David Howells]

Max Kellermann <max.kellermann@ionos.com> wrote:

> When checking whether the edges of adjacent subrequests touch, the
> `prev` variable is deferenced, but it might not have been initialized.
> This causes crashes like this one:
> 
>  BUG: unable to handle page fault for address: 0000000181343843
> ...
> 
> Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
> Cc: stable@vger.kernel.org
> Signed-off-by: Max Kellermann <max.kellermann@ionos.com>

Signed-off-by: David Howells <dhowells@redhat.com>

Patch "fs/netfs/read_collect: fix crash due to uninitialized `prev` variable" has been added to the 6.13-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    fs/netfs/read_collect: fix crash due to uninitialized `prev` variable

to the 6.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     fs-netfs-read_collect-fix-crash-due-to-uninitialized-prev-variable.patch
and it can be found in the queue-6.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-116416-greg=kroah.com@vger.kernel.org Fri Feb 14 14:19:30 2025
From: Max Kellermann <max.kellermann@ionos.com>
Date: Fri, 14 Feb 2025 14:12:25 +0100
Subject: fs/netfs/read_collect: fix crash due to uninitialized `prev` variable
To: dhowells@redhat.com, netfs@lists.linux.dev, linux-kernel@vger.kernel.org
Cc: Max Kellermann <max.kellermann@ionos.com>, stable@vger.kernel.org
Message-ID: <20250214131225.492756-1-max.kellermann@ionos.com>

From: Max Kellermann <max.kellermann@ionos.com>

[ Just like the other two netfs patches I sent yesterday, this one
  doesn't apply to v6.14 as it was obsoleted by commit e2d46f2ec332
  ("netfs: Change the read result collector to only use one work item").  ]

When checking whether the edges of adjacent subrequests touch, the
`prev` variable is deferenced, but it might not have been initialized.
This causes crashes like this one:

 BUG: unable to handle page fault for address: 0000000181343843
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 8000001c66db0067 P4D 8000001c66db0067 PUD 0
 Oops: Oops: 0000 [#1] SMP PTI
 CPU: 1 UID: 33333 PID: 24424 Comm: php-cgi8.2 Kdump: loaded Not tainted 6.13.2-cm4all0-hp+ #427
 Hardware name: HP ProLiant DL380 Gen9/ProLiant DL380 Gen9, BIOS P89 11/23/2021
 RIP: 0010:netfs_consume_read_data.isra.0+0x5ef/0xb00
 Code: fe ff ff 48 8b 83 88 00 00 00 48 8b 4c 24 30 4c 8b 43 78 48 85 c0 48 8d 51 70 75 20 48 8b 73 30 48 39 d6 74 17 48 8b 7c 24 40 <48> 8b 4f 78 48 03 4f 68 48 39 4b 68 0f 84 ab 02 00 00 49 29 c0 48
 RSP: 0000:ffffc90037adbd00 EFLAGS: 00010283
 RAX: 0000000000000000 RBX: ffff88811bda0600 RCX: ffff888620e7b980
 RDX: ffff888620e7b9f0 RSI: ffff88811bda0428 RDI: 00000001813437cb
 RBP: 0000000000000000 R08: 0000000000004000 R09: 0000000000000000
 R10: ffffffff82e070c0 R11: 0000000007ffffff R12: 0000000000004000
 R13: ffff888620e7bb68 R14: 0000000000008000 R15: ffff888620e7bb68
 FS:  00007ff2e0e7ddc0(0000) GS:ffff88981f840000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000181343843 CR3: 0000001bc10ba006 CR4: 00000000001706f0
 Call Trace:
  <TASK>
  ? __die+0x1f/0x60
  ? page_fault_oops+0x15c/0x450
  ? search_extable+0x22/0x30
  ? netfs_consume_read_data.isra.0+0x5ef/0xb00
  ? search_module_extables+0xe/0x40
  ? exc_page_fault+0x5e/0x100
  ? asm_exc_page_fault+0x22/0x30
  ? netfs_consume_read_data.isra.0+0x5ef/0xb00
  ? intel_iommu_unmap_pages+0xaa/0x190
  ? __pfx_cachefiles_read_complete+0x10/0x10
  netfs_read_subreq_terminated+0x24f/0x390
  cachefiles_read_complete+0x48/0xf0
  iomap_dio_bio_end_io+0x125/0x160
  blk_update_request+0xea/0x3e0
  scsi_end_request+0x27/0x190
  scsi_io_completion+0x43/0x6c0
  blk_complete_reqs+0x40/0x50
  handle_softirqs+0xd1/0x280
  irq_exit_rcu+0x91/0xb0
  common_interrupt+0x3b/0xa0
  asm_common_interrupt+0x22/0x40
 RIP: 0033:0x55fe8470d2ab
 Code: 00 00 3c 7e 74 3b 3c b6 0f 84 dd 03 00 00 3c 1e 74 2f 83 c1 01 48 83 c2 38 48 83 c7 30 44 39 d1 74 3e 48 63 42 08 85 c0 79 a3 <49> 8b 46 48 8b 04 38 f6 c4 04 75 0b 0f b6 42 30 83 e0 0c 3c 04 75
 RSP: 002b:00007ffca5ef2720 EFLAGS: 00000216
 RAX: 0000000000000023 RBX: 0000000000000008 RCX: 000000000000001b
 RDX: 00007ff2e0cdb6f8 RSI: 0000000000000006 RDI: 0000000000000510
 RBP: 00007ffca5ef27a0 R08: 00007ffca5ef2720 R09: 0000000000000001
 R10: 000000000000001e R11: 00007ff2e0c10d08 R12: 0000000000000001
 R13: 0000000000000120 R14: 00007ff2e0cb1ed0 R15: 00000000000000b0
  </TASK>

Fixes: ee4cdf7ba857 ("netfs: Speed up buffered reading")
Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/netfs/read_collect.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -258,17 +258,18 @@ donation_changed:
 	 */
 	if (!subreq->consumed &&
 	    !prev_donated &&
-	    !list_is_first(&subreq->rreq_link, &rreq->subrequests) &&
-	    subreq->start == prev->start + prev->len) {
+	    !list_is_first(&subreq->rreq_link, &rreq->subrequests)) {
 		prev = list_prev_entry(subreq, rreq_link);
-		WRITE_ONCE(prev->next_donated, prev->next_donated + subreq->len);
-		subreq->start += subreq->len;
-		subreq->len = 0;
-		subreq->transferred = 0;
-		trace_netfs_donate(rreq, subreq, prev, subreq->len,
-				   netfs_trace_donate_to_prev);
-		trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
-		goto remove_subreq_locked;
+		if (subreq->start == prev->start + prev->len) {
+			WRITE_ONCE(prev->next_donated, prev->next_donated + subreq->len);
+			subreq->start += subreq->len;
+			subreq->len = 0;
+			subreq->transferred = 0;
+			trace_netfs_donate(rreq, subreq, prev, subreq->len,
+					   netfs_trace_donate_to_prev);
+			trace_netfs_sreq(subreq, netfs_sreq_trace_donate_to_prev);
+			goto remove_subreq_locked;
+		}
 	}
 
 	/* If we can't donate down the chain, donate up the chain instead. */


Patches currently in stable-queue which might be from max.kellermann@ionos.com are

queue-6.13/fs-netfs-read_collect-fix-crash-due-to-uninitialized-prev-variable.patch
queue-6.13/fs-netfs-read_pgpriv2-skip-folio-queues-without-marks3.patch

Re: [PATCH v6.13 v2] fs/netfs/read_collect: fix crash due to uninitialized `prev` variable

[Johannes Berg]

On Fri, 2025-02-14 at 14:12 +0100, Max Kellermann wrote:
> When checking whether the edges of adjacent subrequests touch, the
> `prev` variable is deferenced, but it might not have been initialized.
> This causes crashes like this one:

[...]

I believe we also need this in 6.12?

johannes

Re: [PATCH v6.13 v2] fs/netfs/read_collect: fix crash due to uninitialized `prev` variable

[Greg Kroah-Hartman]

On Fri, Mar 07, 2025 at 03:27:41PM +0100, Johannes Berg wrote:
> On Fri, 2025-02-14 at 14:12 +0100, Max Kellermann wrote:
> > When checking whether the edges of adjacent subrequests touch, the
> > `prev` variable is deferenced, but it might not have been initialized.
> > This causes crashes like this one:
> 
> [...]
> 
> I believe we also need this in 6.12?

Now added, thanks.

greg k-h