[syzbot] [v9fs?] WARNING in v9fs_init_request (2)

[syzbot] [v9fs?] WARNING in v9fs_init_request (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    1590cf032971 Linux 7.2-rc4
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1446a746580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=48ef5c5c0f192153
dashboard link: https://syzkaller.appspot.com/bug?extid=344c09c64fcd8d3d2782
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1632bc32580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13e0b789580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-1590cf03.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3ad7477f3064/vmlinux-1590cf03.xz
kernel image: https://storage.googleapis.com/syzbot-assets/8e7a9174d4d6/bzImage-1590cf03.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+344c09c64fcd8d3d2782@syzkaller.appspotmail.com

------------[ cut here ]------------
folio expected an open fid inode->i_ino=4580113
WARNING: fs/9p/vfs_addr.c:168 at v9fs_init_request+0x451/0x540 fs/9p/vfs_addr.c:168, CPU#2: syz.0.21/5945
Modules linked in:
CPU: 2 UID: 0 PID: 5945 Comm: syz.0.21 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:v9fs_init_request+0x455/0x540 fs/9p/vfs_addr.c:168
Code: 48 b8 00 00 00 00 00 fc ff df 48 8d 7b 40 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 db 00 00 00 48 8d 3d bf b1 20 0d 48 8b 73 40 <67> 48 0f b9 3a bb ea ff ff ff e9 41 fe ff ff e8 f7 98 ff fd be 02
RSP: 0018:ffffc90003c5f778 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff888056c2d240 RCX: ffffffff840a4337
RDX: 1ffff1100ad85a50 RSI: 0000000004580113 RDI: ffffffff912af550
RBP: fffffffffffffffe R08: 0000000000000007 R09: fffffffffffff000
R10: fffffffffffffffe R11: 0000000000000000 R12: ffff888038e04178
R13: ffff888050c78e41 R14: ffff888050c78bd0 R15: ffff888056c2d240
FS:  00007ff5dd1fe6c0(0000) GS:ffff8880d5fe6000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff5dd1bbff8 CR3: 000000003d81d000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 netfs_alloc_request+0x71c/0xcb0 fs/netfs/objects.c:72
 netfs_read_folio+0x20c/0x13f0 fs/netfs/buffered_read.c:513
 filemap_read_folio+0xfc/0x3b0 mm/filemap.c:2510
 do_read_cache_folio+0x2d7/0x6b0 mm/filemap.c:4140
 read_mapping_folio include/linux/pagemap.h:1015 [inline]
 __page_get_link.isra.0+0x30/0x350 fs/namei.c:6336
 page_get_link+0x44/0xf0 fs/namei.c:6366
 v9fs_vfs_get_link_dotl+0x27b/0x310 fs/9p/vfs_inode_dotl.c:930
 pick_link+0xd17/0x13c0 fs/namei.c:2068
 step_into_slowpath+0x9ba/0xf90 fs/namei.c:2127
 step_into fs/namei.c:2152 [inline]
 walk_component fs/namei.c:2288 [inline]
 lookup_last fs/namei.c:2789 [inline]
 path_lookupat+0x58b/0xc40 fs/namei.c:2813
 filename_lookup+0x202/0x590 fs/namei.c:2842
 user_path_at+0x3c/0x60 fs/namei.c:3641
 do_mount fs/namespace.c:4171 [inline]
 __do_sys_mount fs/namespace.c:4390 [inline]
 __se_sys_mount fs/namespace.c:4367 [inline]
 __x64_sys_mount+0x1fb/0x310 fs/namespace.c:4367
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff5ddb9de99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff5dd1fe028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ff5dde25fa0 RCX: 00007ff5ddb9de99
RDX: 00002000000004c0 RSI: 0000200000000480 RDI: 0000000000000000
RBP: 00007ff5ddc33eaf R08: 0000200000000c00 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff5dde26038 R14: 00007ff5dde25fa0 R15: 00007ffc18202cd8
 </TASK>
----------------
Code disassembly (best guess):
   0:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
   7:	fc ff df
   a:	48 8d 7b 40          	lea    0x40(%rbx),%rdi
   e:	48 89 fa             	mov    %rdi,%rdx
  11:	48 c1 ea 03          	shr    $0x3,%rdx
  15:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
  19:	0f 85 db 00 00 00    	jne    0xfa
  1f:	48 8d 3d bf b1 20 0d 	lea    0xd20b1bf(%rip),%rdi        # 0xd20b1e5
  26:	48 8b 73 40          	mov    0x40(%rbx),%rsi
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	bb ea ff ff ff       	mov    $0xffffffea,%ebx
  34:	e9 41 fe ff ff       	jmp    0xfffffe7a
  39:	e8 f7 98 ff fd       	call   0xfdff9935
  3e:	be                   	.byte 0xbe
  3f:	02                   	.byte 0x2


---
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Forwarded: [PATCH] 9p: add DIAG WARN_ONCE sites to disambiguate v9fs_init_request no_fid failures

[syzbot]

For archival purposes, forwarding an incoming command email to
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***

Subject: [PATCH] 9p: add DIAG WARN_ONCE sites to disambiguate v9fs_init_request no_fid failures
Author: kartikey406@gmail.com

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


v9fs_init_request() funnels four different failure modes into a
single shared WARN_ONCE("folio expected an open fid ...") message,
making it impossible to tell from a crash report which one actually
fired. Split each site out with its own message (and the errno for
the v9fs_fid_lookup() case) to identify the exact cause of the
syzbot-reported "WARNING in v9fs_init_request (2)".

Diagnostic only, not a functional fix.

Reported-by: syzbot+344c09c64fcd8d3d2782@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/9p/vfs_addr.c | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/fs/9p/vfs_addr.c b/fs/9p/vfs_addr.c
index 1ac0b3dcc077..fc05bd963506 100644
--- a/fs/9p/vfs_addr.c
+++ b/fs/9p/vfs_addr.c
@@ -136,21 +136,37 @@ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 
 	if (file) {
 		fid = file->private_data;
-		if (!fid)
-			goto no_fid;
+		if (!fid) {
+			WARN_ONCE(1, "DIAG: v9fs_init_request: file has no fid, "
+			           "inode->i_ino=%llx\n", rreq->inode->i_ino);
+			return -EINVAL;
+		}
 		p9_fid_get(fid);
 	} else if (S_ISLNK(rreq->inode->i_mode)) {
 		dentry = d_find_any_alias(rreq->inode);
-		if (!dentry)
-			goto no_fid;
+		if (!dentry) {
+			WARN_ONCE(1, "DIAG: v9fs_init_request: symlink inode has no "
+				  "dentry alias, inode->i_ino=%llx\n",
+				   rreq->inode->i_ino);
+			return -EINVAL;
+		}
 		fid = v9fs_fid_lookup(dentry);
+		if (IS_ERR(fid)) {
+			WARN_ONCE(1, "DIAG: v9fs_init_request: v9fs_fid_lookup failed "
+				"for symlink, err=%ld dentry=%pd4 inode->i_ino=%llx\n",
+			 	PTR_ERR(fid), dentry, rreq->inode->i_ino);
+			dput(dentry);
+			return PTR_ERR(fid);
+		}
 		dput(dentry);
-		if (IS_ERR(fid))
-			goto no_fid;
 	} else {
 		fid = v9fs_fid_find_inode(rreq->inode, writing, INVALID_UID, true);
-		if (!fid)
-			goto no_fid;
+		if (!fid) {
+			WARN_ONCE(1, "DIAG: v9fs_init_request: non-symlink inode has "
+				   "no open/writeback fid, inode->i_ino=%llx\n",
+				   rreq->inode->i_ino);
+			return -EINVAL;
+		}
 	}
 
 	rreq->wsize = fid->clnt->msize - P9_IOHDRSZ;
@@ -163,11 +179,6 @@ static int v9fs_init_request(struct netfs_io_request *rreq, struct file *file)
 	WARN_ON(rreq->origin == NETFS_READ_FOR_WRITE && !(fid->mode & P9_ORDWR));
 	rreq->netfs_priv = fid;
 	return 0;
-
-no_fid:
-	WARN_ONCE(1, "folio expected an open fid inode->i_ino=%llx\n",
-		  rreq->inode->i_ino);
-	return -EINVAL;
 }
 
 /**
-- 
2.43.0