From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	sashiko-bot <sashiko-bot@kernel.org>,
	Ian Rogers <irogers@google.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.1 0562/1067] perf symbols: Break infinite loop on zero-filled notes in sysfs__read_build_id()
Date: Tue, 21 Jul 2026 17:19:23 +0200
Message-ID: <20260721152437.176904489@linuxfoundation.org>
In-Reply-To: <20260721152424.521567757@linuxfoundation.org>
References: <20260721152424.521567757@linuxfoundation.org>
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6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Arnaldo Carvalho de Melo <acme@redhat.com>

[ Upstream commit 063c647b24f640657d6d9e2e90d620ea3ee19ae6 ]

sysfs__read_build_id() iterates ELF note headers from sysfs files in a
while(1) loop.  If the file contains a zero-filled note header (both
n_namesz and n_descsz are 0), the code computes n = namesz + descsz = 0
and calls read(fd, bf, 0).  read() with count 0 returns 0, which
matches the expected (ssize_t)n value, so the error check passes and
the loop repeats — reading the same zero bytes and spinning forever.

This can happen with corrupted or zero-padded sysfs pseudo-files.

Add a check for n == 0 before the read, since no valid ELF note has
both name and description of zero length.

Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Fixes: f1617b40596cb341 ("perf symbols: Record the build_ids of kernel modules too")
Reviewed-by: Ian Rogers <irogers@google.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 tools/perf/util/symbol-elf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 0b8956740fd8ac..7e1b62388f0b72 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -723,6 +723,9 @@ int sysfs__read_build_id(const char *filename, struct build_id *bid)
 			} else {
 				n = namesz + descsz;
 			}
+			/* no valid note has both namesz and descsz zero */
+			if (n == 0)
+				break;
 			if (read(fd, bf, n) != (ssize_t)n)
 				break;
 		}
-- 
2.53.0