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Prevent null dereferences when accessing dbuf kstat

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In arc_buf_info(), the arc_buf_t may have no header.  If not, don't try
to fetch the arc buffer stats and instead just zero them.

The null dereferences were observed while accessing the dbuf kstat with
awk on a system in which millions of small files were being created in
order to overflow the system's metadata limit.

Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes #4837
This commit is contained in:
Tim Chase 2016-07-10 09:09:02 -05:00 committed by Brian Behlendorf
parent 8d9e124515
commit 8887c7d778
1 changed files with 7 additions and 3 deletions
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10
module/zfs/arc.c
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@ -1461,6 +1461,13 @@ arc_buf_info(arc_buf_t *ab, arc_buf_info_t *abi, int state_index)
l2arc_buf_hdr_t *l2hdr = NULL;
arc_state_t *state = NULL;
memset(abi, 0, sizeof (arc_buf_info_t));
if (hdr == NULL)
return;
abi->abi_flags = hdr->b_flags;
if (HDR_HAS_L1HDR(hdr)) {
l1hdr = &hdr->b_l1hdr;
state = l1hdr->b_state;
@ -1468,9 +1475,6 @@ arc_buf_info(arc_buf_t *ab, arc_buf_info_t *abi, int state_index)
if (HDR_HAS_L2HDR(hdr))
l2hdr = &hdr->b_l2hdr;
memset(abi, 0, sizeof (arc_buf_info_t));
abi->abi_flags = hdr->b_flags;
if (l1hdr) {
abi->abi_datacnt = l1hdr->b_datacnt;
abi->abi_access = l1hdr->b_arc_access;