The mdadm program controls Linux md devices (software RAID arrays)
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From 548e9b916f86c06e2cdb50d8f49633f9bec66c7e Mon Sep 17 00:00:00 2001
From: Logan Gunthorpe <>
Date: Wed, 22 Jun 2022 14:25:09 -0600
Subject: [PATCH 34/52] mdadm/Grow: Fix use after close bug by closing after
The test 07reshape-grow fails most of the time. But it succeeds around
1 in 5 times. When it does succeed, it causes the tests to die because
mdadm has segfaulted.
The segfault was caused by mdadm attempting to repoen a file
descriptor that was already closed. The backtrace of the segfault
#0 __strncmp_avx2 () at ../sysdeps/x86_64/multiarch/strcmp-avx2.S:101
#1 0x000056146e31d44b in devnm2devid (devnm=0x0) at util.c:956
#2 0x000056146e31dab4 in open_dev_flags (devnm=0x0, flags=0)
at util.c:1072
#3 0x000056146e31db22 in open_dev (devnm=0x0) at util.c:1079
#4 0x000056146e3202e8 in reopen_mddev (mdfd=4) at util.c:2244
#5 0x000056146e329f36 in start_array (mdfd=4,
mddev=0x7ffc55342450 "/dev/md0", content=0x7ffc55342860,
st=0x56146fc78660, ident=0x7ffc55342f70, best=0x56146fc6f5d0,
bestcnt=10, chosen_drive=0, devices=0x56146fc706b0, okcnt=5,
sparecnt=0, rebuilding_cnt=0, journalcnt=0, c=0x7ffc55342e90,
clean=1, avail=0x56146fc78720 "\001\001\001\001\001",
start_partial_ok=0, err_ok=0, was_forced=0)
at Assemble.c:1206
#6 0x000056146e32c36e in Assemble (st=0x56146fc78660,
mddev=0x7ffc55342450 "/dev/md0", ident=0x7ffc55342f70,
devlist=0x56146fc6e2d0, c=0x7ffc55342e90)
at Assemble.c:1914
#7 0x000056146e312ac9 in main (argc=11, argv=0x7ffc55343238)
at mdadm.c:1510
The file descriptor was closed early in Grow_continue(). The noted commit
moved the close() call to close the fd above the fork which caused the
parent process to return with a closed fd.
This meant reshape_array() and Grow_continue() would return in the parent
with the fd forked. The fd would eventually be passed to reopen_mddev()
which returned an unhandled NULL from fd2devnm() which would then be
dereferenced in devnm2devid.
Fix this by moving the close() call below the fork. This appears to
fix the 07revert-grow test. While we're at it, switch to using
close_fd() to invalidate the file descriptor.
Fixes: 77b72fa82813 ("mdadm/Grow: prevent md's fd from being occupied during delayed time")
Cc: Alex Wu <>
Cc: BingJing Chang <>
Cc: Danny Shih <>
Cc: ChangSyun Peng <>
Signed-off-by: Logan Gunthorpe <>
Acked-by: Mariusz Tkaczyk <>
Signed-off-by: Jes Sorensen <>
Grow.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/Grow.c b/Grow.c
index 8c520d42..97f22c75 100644
--- a/Grow.c
+++ b/Grow.c
@@ -3514,7 +3514,6 @@ started:
return 0;
- close(fd);
/* Now we just need to kick off the reshape and watch, while
* handling backups of the data...
* This is all done by a forked background process.
@@ -3535,6 +3534,9 @@ started:
+ /* Close unused file descriptor in the forked process */
+ close_fd(&fd);
/* If another array on the same devices is busy, the
* reshape will wait for them. This would mean that
* the first section that we suspend will stay suspended