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loop: fix a race when a free loop device is snatched

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When /dev/loop-control exists and *device is empty,
the mount may fail if a concurrent mount is running.

function                                             old     new   delta
set_loop                                             809     807      -2

Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Xiaoming Ni 2022-11-15 14:54:05 +01:00 committed by Denys Vlasenko
parent 707a7ef4c7
commit cb8d2ea8c9
1 changed files with 10 additions and 1 deletions
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11
libbb/loop.c
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@ -218,8 +218,17 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
} }
/* failure, undo LOOP_SET_FD */ /* failure, undo LOOP_SET_FD */
ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary ioctl(lfd, LOOP_CLR_FD, 0); // actually, 0 param is unnecessary
} else {
/* device is not free (rc == 0), or error other than ENXIO */
if (rc == 0 /* device is not free? */
&& !*device /* racing with other mount? */
&& try != dev /* tried a _kernel-offered_ loopN? */
) {
free(try);
close(lfd);
goto get_free_loopN;
}
} }
/* else: device is not free (rc == 0) or error other than ENXIO */
close_and_try_next_loopN: close_and_try_next_loopN:
close(lfd); close(lfd);
try_next_loopN: try_next_loopN: