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devtmpfs: fix theoretical stale pointer deref in devtmpfsd() 

After complete(&setup_done), devtmpfs_init proceeds and may actually
return, invalidating the *err pointer, before devtmpfsd() proceeds to
reading back *err.

This is of course completely theoretical since the error conditions
never trigger in practice, and even if they did, nobody cares about
the exit value from a kernel thread, so it doesn't matter if we happen
to read back some garbage from some other stack frame. Still, this
isn't a pattern that should be copy-pasted, so fix it.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/r/20200115184154.3492-2-linux@rasmusvillemoes.dk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Rasmus Villemoes 2020-01-15 19:41:49 +01:00 committed by Greg Kroah-Hartman
parent 0707cfa5c3
commit c9d6b287d7
1 changed files with 8 additions and 6 deletions
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14
drivers/base/devtmpfs.c
View File

@ -390,12 +390,13 @@ static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
static int devtmpfsd(void *p)
{
int *err = p;
*err = ksys_unshare(CLONE_NEWNS);
if (*err)
int err;
err = ksys_unshare(CLONE_NEWNS);
if (err)
goto out;
*err = do_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
if (*err)
err = do_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
if (err)
goto out;
ksys_chdir("/.."); /* will traverse into overmounted root */
ksys_chroot(".");
@ -421,8 +422,9 @@ static int devtmpfsd(void *p)
}
return 0;
out:
*(int *)p = err;
complete(&setup_done);
return *err;
return err;
}
/*