[PATCH 5.15 214/843] afs: fix NULL pointer dereference in afs_get_tree()

[Greg Kroah-Hartman]

5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matvey Kovalev <matvey.kovalev at ispras.ru>

commit 0b70716081c6462be9b2928ad736d0d527b09678 upstream.

afs_alloc_sbi() uses kzalloc for memory allocation. And, if
ctx->dyn_root is not null, as->cell and as->volume are null.
In trace_afs_get_tree() they are dereferenced.

KASAN error message:

KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 2 PID: 18478 Comm: syz-executor.7 Not tainted 5.10.246-syzkaller #0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1
04/01/2014
RIP: 0010:perf_trace_afs_get_tree+0x1d9/0x550
include/trace/events/afs.h:1365

Call Trace:
trace_afs_get_tree include/trace/events/afs.h:1365 [inline]
afs_get_tree+0x922/0x1350 fs/afs/super.c:599
vfs_get_tree+0x8e/0x300 fs/super.c:1572
do_new_mount fs/namespace.c:3011 [inline]
path_mount+0x14a5/0x2220 fs/namespace.c:3341
do_mount fs/namespace.c:3354 [inline]
__do_sys_mount fs/namespace.c:3562 [inline]
__se_sys_mount fs/namespace.c:3539 [inline]
__x64_sys_mount+0x283/0x300 fs/namespace.c:3539
 do_syscall_64+0x33/0x50 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x67/0xd1

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 80548b03991f5 ("afs: Add more tracepoints")
Cc: stable at vger.kernel.org
Signed-off-by: Matvey Kovalev <matvey.kovalev at ispras.ru>
Signed-off-by: David Howells <dhowells at redhat.com>
Link: https://patch.msgid.link/20260622090856.2746629-4-dhowells@redhat.com
cc: Marc Dionne <marc.dionne at auristor.com>
cc: linux-afs at lists.infradead.org
Signed-off-by: Christian Brauner (Amutable) <brauner at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 fs/afs/super.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -596,7 +596,8 @@ static int afs_get_tree(struct fs_contex
 	}
 
 	fc->root = dget(sb->s_root);
-	trace_afs_get_tree(as->cell, as->volume);
+	if (!ctx->dyn_root)
+		trace_afs_get_tree(as->cell, as->volume);
 	_leave(" = 0 [%p]", sb);
 	return 0;