pkg/report: improve guilty file identification

Previously we would pick the first non-ignored file. Now instead,
continue searching the stack trace for more specific files.

A "more specific" file wrt the first non-ignored file has:
  - the same directory prefix
  - a deeper directory nesting
E.g. `fs/ntfs3/*.c` is "more specific" than "fs/*.c".
We search for the most specific file (i.e. the deepest nesting), and
take the first most specific if there are multiple files with the same
nesting.

This commit also adds three tests for this behaviour, taken from
recent `syzbot` bugs which identified the wrong file. Now the desired
file is identified.

Only one existing test shows different output with the new behaviour.

Updates #3393.

1 files changed, 82 insertions, 0 deletions

diff --git a/pkg/report/testdata/linux/guilty/55 b/pkg/report/testdata/linux/guilty/55
new file mode 100644
index 000000000..bfbaad02f
--- /dev/null
+++ b/pkg/report/testdata/linux/guilty/55
@@ -0,0 +1,82 @@
+FILE: fs/ntfs/super.c
+
+loop4: detected capacity change from 0 to 264192
+==================================
+WARNING: Nested lock was not taken
+6.0.0-rc6-syzkaller-17742-gc194837ebb57 #0 Not tainted
+----------------------------------
+syz-executor253/3315 is trying to lock:
+ffff0000c495a9d8 (&s->s_inode_list_lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:349 [inline]
+ffff0000c495a9d8 (&s->s_inode_list_lock){+.+.}-{2:2}, at: inode_sb_list_del fs/inode.c:503 [inline]
+ffff0000c495a9d8 (&s->s_inode_list_lock){+.+.}-{2:2}, at: evict+0x90/0x334 fs/inode.c:654
+
+but this task is not holding:
+Unable to handle kernel paging request at virtual address 0000000100000017
+Mem abort info:
+  ESR = 0x0000000096000005
+  EC = 0x25: DABT (current EL), IL = 32 bits
+  SET = 0, FnV = 0
+  EA = 0, S1PTW = 0
+  FSC = 0x05: level 1 translation fault
+Data abort info:
+  ISV = 0, ISS = 0x00000005
+  CM = 0, WnR = 0
+user pgtable: 4k pages, 48-bit VAs, pgdp=000000010a8da000
+[0000000100000017] pgd=0800000107ed2003, p4d=0800000107ed2003, pud=0000000000000000
+Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
+Modules linked in:
+CPU: 0 PID: 3315 Comm: syz-executor253 Not tainted 6.0.0-rc6-syzkaller-17742-gc194837ebb57 #0
+Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022
+pstate: 604000c5 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
+pc : print_lock_nested_lock_not_held kernel/locking/lockdep.c:4885 [inline]
+pc : __lock_acquire+0x7cc/0x30a4 kernel/locking/lockdep.c:5044
+lr : print_lock_nested_lock_not_held kernel/locking/lockdep.c:4884 [inline]
+lr : __lock_acquire+0x7c0/0x30a4 kernel/locking/lockdep.c:5044
+sp : ffff80001289b8b0
+x29: ffff80001289b990 x28: 0000000000000001 x27: ffff80000d30c000
+x26: ffff0000c68d24b8 x25: ffff0000c68d24d8 x24: 0000000000000002
+x23: ffff0000c68d24d0 x22: ffff80000d32a753 x21: ffff80000d32a712
+x20: 0000000000040067 x19: ffff0000c68d1a80 x18: 0000000000000156
+x17: 2b7463697665203a x16: 0000000000000002 x15: 0000000000000000
+x14: 0000000000000000 x13: 205d353133335420 x12: 5b5d303434313530
+x11: ff808000081c1630 x10: 0000000000000000 x9 : 30785d1575e13b00
+x8 : 00000000ffffffff x7 : 205b5d3034343135 x6 : ffff800008195d30
+x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
+x2 : 0000000000000000 x1 : 0000000100000001 x0 : ffff80000cb555a1
+Call trace:
+ print_lock_nested_lock_not_held kernel/locking/lockdep.c:4885 [inline]
+ __lock_acquire+0x7cc/0x30a4 kernel/locking/lockdep.c:5044
+ lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5666
+ __raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
+ _raw_spin_lock+0x54/0x6c kernel/locking/spinlock.c:154
+ spin_lock include/linux/spinlock.h:349 [inline]
+ inode_sb_list_del fs/inode.c:503 [inline]
+ evict+0x90/0x334 fs/inode.c:654
+ iput_final fs/inode.c:1748 [inline]
+ iput+0x2c4/0x324 fs/inode.c:1774
+ ntfs_fill_super+0x1254/0x14a4 fs/ntfs/super.c:188
+ get_tree_bdev+0x1e8/0x2a0 fs/super.c:1323
+ ntfs_fs_get_tree+0x28/0x38 fs/ntfs3/super.c:1358
+ vfs_get_tree+0x40/0x140 fs/super.c:1530
+ do_new_mount+0x1dc/0x4e4 fs/namespace.c:3040
+ path_mount+0x358/0x914 fs/namespace.c:3370
+ do_mount fs/namespace.c:3383 [inline]
+ __do_sys_mount fs/namespace.c:3591 [inline]
+ __se_sys_mount fs/namespace.c:3568 [inline]
+ __arm64_sys_mount+0x2c4/0x3c4 fs/namespace.c:3568
+ __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
+ invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
+ el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
+ do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
+ el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
+ el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
+ el0t_64_sync+0x18c/0x190
+Code: 94f84769 f94002e8 d0024dc0 91168400 (f9400d01) 
+---[ end trace 0000000000000000 ]---
+----------------
+Code disassembly (best guess):
+   0:	94f84769 	bl	0x3e11da4
+   4:	f94002e8 	ldr	x8, [x23]
+   8:	d0024dc0 	adrp	x0, 0x49ba000
+   c:	91168400 	add	x0, x0, #0x5a1
+* 10:	f9400d01 	ldr	x1, [x8, #24] <-- trapping instruction
\ No newline at end of file