+ taskstats-fix-cpumask-parsing-cutting-off-the-last-character.patch added to mm-nonmm-unstable branch

The patch titled
     Subject: taskstats: fix cpumask parsing cutting off the last character
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     taskstats-fix-cpumask-parsing-cutting-off-the-last-character.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/taskstats-fix-cpumask-parsing-cutting-off-the-last-character.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Bradley Morgan <[email protected]>
Subject: taskstats: fix cpumask parsing cutting off the last character
Date: Thu, 23 Jul 2026 21:09:22 +0000

parse() hands nla_strscpy() len as dstsize, and nla_strscpy() copies at
most dstsize - 1 bytes.  When the attr payload comes in without a trailing
NUL, srclen == len >= dstsize and the last character of the cpumask string
gets cut off.  Register "0-15" and you are silently listening on "0-1",
exit data for the rest never shows up.

The bug only bites when the sender doesnt NUL terminate the payload;
senders that include the NUL were always fine (srclen gets decremented for
the trailing NUL, so srclen < dstsize).  Thats probably why this survived
20 years.  And the policy is NLA_STRING, not NLA_NUL_STRING, so a payload
without the trailing NUL is legit input here.

Skip the kmalloc/nla_strscpy dance entirely and use nla_strdup(), which
already allocates srclen + 1 and terminates.  The nla_len() bounds checks
stay as they were.

Link: https://lore.kernel.org/[email protected]
Fixes: f9fd8914c1ac ("[PATCH] per-task delay accounting taskstats interface: control exit data through cpumasks")
Signed-off-by: Bradley Morgan <[email protected]>
Reported-by: Oleg Deomi <[email protected]>
Closes: https://lore.kernel.org/CAByWkfZ6b1=3H9pwkz-dDQOs9cZaF-HYQ6b9Yb0=Hq2r1Vv_Pw@mail.gmail.com
Reviewed-by: Andrew Morton <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 kernel/taskstats.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/kernel/taskstats.c~taskstats-fix-cpumask-parsing-cutting-off-the-last-character
+++ a/kernel/taskstats.c
@@ -368,10 +368,9 @@ static int parse(struct nlattr *na, stru
 		return -E2BIG;
 	if (len < 1)
 		return -EINVAL;
-	data = kmalloc(len, GFP_KERNEL);
+	data = nla_strdup(na, GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
-	nla_strscpy(data, na, len);
 	ret = cpulist_parse(data, mask);
 	kfree(data);
 	return ret;
_

Patches currently in -mm which might be from [email protected] are

lib-string-fix-memchr_inv-for-large-ranges.patch
signal-avoid-shared-siginfo-namespace-rewrites.patch
taskstats-fix-cpumask-parsing-cutting-off-the-last-character.patch