linux-kernel - [PATCH] xfs: fix a NULL pointer problem

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Date: Thu, 20 Jun 2024 15:43:13 +0800
From: shaozongfan <shaozongfan@...inos.cn>
To: chandan.babu@...cle.com,
	djwong@...nel.org
Cc: linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	shaozongfan <shaozongfan@...inos.cn>
Subject: [PATCH] xfs: fix a NULL pointer problem

when a process using getdents64() api to get a Folder inside
the file directory,meantime other process delete the file
directory.it would cause an error like this:

[  100.640099] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000001
[  100.641246] Mem abort info:
[  100.641636]   ESR = 0x96000007
[  100.642057]   Exception class = DABT (current EL), IL = 32 bits
[  100.642815]   SET = 0, FnV = 0
[  100.643235]   EA = 0, S1PTW = 0
[  100.643664] Data abort info:
[  100.644063]   ISV = 0, ISS = 0x00000007
[  100.644574]   CM = 0, WnR = 0
[  100.644984] user pgtable: 64k pages, 48-bit VAs, pgdp = 00000000135105a5
[  100.645876] [0000000000000001] pgd=00000001ac6b0003, pud=00000001ac6b0003, pmd=00000001aad30003, pte=0000000000000000
[  100.647204] Internal error: Oops: 96000007 [#1] SMP
[  100.647843] Modules linked in: binfmt_misc fuse devlink xt_CHECKSUM ipt_MASQUERADE ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ip6table_nat nf_nat_ipv6 ip6table_mangle tun bridge ip6table_raw ip6table_security stp llc iptable_nat nf_nat_ipv4 nf_nat iptable_mangle iptable_raw iptable_security nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter sch_fq_codel sunrpc vfat fat ip_tables sr_mod cdrom virtio_gpu virtio_console virtio_net virtio_scsi net_failover failover dm_mirror dm_region_hash dm_log gb
[  100.654877] Process getdents (pid: 6455, stack limit = 0x00000000a8241109)
[  100.655759] CPU: 0 PID: 6455 Comm: getdents Kdump: loaded Tainted: P           OE     4.19.90-25.10.v2101.ky10.aarch64 #1
[  100.657418] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
[  100.658484] pstate: 80000005 (Nzcv daif -PAN -UAO)
[  100.659297] pc : xfs_dir2_sf_get_parent_ino+0x1c/0x30
[  100.660093] lr : xfs_dir2_sf_getdents.isra.0+0xd8/0x248
[  100.660922] sp : ffff80016eda3bd0
[  100.661476] x29: ffff80016eda3bd0 x28: ffff800167c4d900
[  100.662310] x27: 0000000000000000 x26: 0000000000000000
[  100.663149] x25: 0000000000000000 x24: ffff800174ca5000
[  100.663980] x23: 000000000000000a x22: 0000000000000000
[  100.664822] x21: ffff800161337780 x20: ffff8001437b8000
[  100.665647] x19: 0000000000000000 x18: 0000000000000000
[  100.666482] x17: 0000000000000001 x16: 0000000000000000
[  100.667328] x15: 0000000000000000 x14: 0000000000000000
[  100.668159] x13: 0000000000000000 x12: 0000000000000000
[  100.668985] x11: 0000000000000000 x10: 0000000000000000
[  100.669816] x9 : 0000000000000000 x8 : 0000000000000000
[  100.670643] x7 : 0000000000000000 x6 : ffff8001704a6414
[  100.671517] x5 : 0000000000000004 x4 : 0000000004195704
[  100.672355] x3 : 000000000000002e x2 : 0000000000000001
[  100.673181] x1 : 0000000000000002 x0 : ffff0000084cda20
[  100.674007] Call trace:
[  100.674427]  xfs_dir2_sf_get_parent_ino+0x1c/0x30
[  100.675168]  xfs_dir2_sf_getdents.isra.0+0xd8/0x248
[  100.675943]  xfs_readdir+0x184/0x1d0
[  100.676522]  xfs_file_readdir+0x40/0x50
[  100.677149]  iterate_dir+0x8c/0x1a8
[  100.677717]  ksys_getdents64+0xb4/0x348
[  100.678335]  __arm64_sys_getdents64+0x28/0x38
[  100.679027]  el0_svc_common+0x78/0x130
[  100.679640]  el0_svc_handler+0x38/0x78
[  100.680249]  el0_svc+0x8/0x1b0
[  100.680756] Code: aa0003f3 aa1e03e0 d503201f 91000a61 (39400660)
[  100.681720] SMP: stopping secondary CPUs
[  100.684250] Starting crashdump kernel...
[  100.684868] Bye!

Signed-off-by: shaozongfan <shaozongfan@...inos.cn>
---
 fs/xfs/xfs_dir2_readdir.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
index 9f3ceb461515..db6c910cad96 100644
--- a/fs/xfs/xfs_dir2_readdir.c
+++ b/fs/xfs/xfs_dir2_readdir.c
@@ -51,7 +51,7 @@ xfs_dir2_sf_getdents(
 	struct xfs_mount	*mp = dp->i_mount;
 	xfs_dir2_dataptr_t	off;		/* current entry's offset */
 	xfs_dir2_sf_entry_t	*sfep;		/* shortform directory entry */
-	xfs_dir2_sf_hdr_t	*sfp;		/* shortform structure */
+	xfs_dir2_sf_hdr_t	*sfp, *sfp1;		/* shortform structure */
 	xfs_dir2_dataptr_t	dot_offset;
 	xfs_dir2_dataptr_t	dotdot_offset;
 	xfs_ino_t		ino;
@@ -93,7 +93,10 @@ xfs_dir2_sf_getdents(
 	 * Put .. entry unless we're starting past it.
 	 */
 	if (ctx->pos <= dotdot_offset) {
-		ino = xfs_dir2_sf_get_parent_ino(sfp);
+		sfp1 = sfp;
+		if (sfp1 == NULL)
+			return 0;
+		ino = xfs_dir2_sf_get_parent_ino(sfp1);
 		ctx->pos = dotdot_offset & 0x7fffffff;
 		if (!dir_emit(ctx, "..", 2, ino, DT_DIR))
 			return 0;
-- 
2.25.1