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Tue, 06 Oct 2026 15:15:15 -0700 (PDT) Received: from com-75606.corp.openai.org ([199.47.143.7]) by smtp.gmail.com with ESMTPSA id 586e51a60fabf-4a2571cab91sm565412fac.11.2026.10.06.15.15.13 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 06 Oct 2026 15:15:14 -0700 (PDT) From: Kyle Zeng To: linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kees@kernel.org, outbounddisclosures@openai.com, Kyle Zeng , stable@vger.kernel.org Subject: [PATCH] exec: snapshot the dentry name before setting task comm Date: Tue, 6 Oct 2026 15:15:11 -0700 Message-ID: <20261006221511.35798-1-kylebot@openai.com> X-Mailer: git-send-email 2.55.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 5111F1C000A X-Rspam-User: X-Stat-Signature: 17cpo9eyg49uewy6jnsonauy1ofq3de5 X-HE-Tag: 1791324916-367029 X-HE-Meta: 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 UDwQTrJk pfJL/+DCIBolTRFXpgVz5BR/qrRRpEHtDpXBE5/vd2AQQYd8TNrjIGRMLKoybEBlq9yCC7p+5dMIbow0DaS36CKk9eMTcvT+vDa9YZNhvFws+2XXm3WnSepA0MeMWdPGqlgIra5vzsXDOmAi34NCLwBSzFxm162UhjJi4CX8eA6t+Dvx/jVe1kuBIcm5AeQJCgX4XlSrrR+vRR/mhn89c/+S6WAAj1XNMu8UXAOv4XjzBIP7tTjXAaLJQBjzaKQad7QyhkkssmYaN+OSepqOgNilyHWOul4bE2n3lSK1d/NrJqwvkXCRx+q+F0+ztk8vE7dbMjawcghglvB6OryzO2oSQPQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: For an empty execveat() pathname, begin_new_exec() passes a live dentry name to __set_task_comm(). RCU keeps the name allocation alive, but does not prevent a concurrent rename from changing an inline name. __set_task_comm() measures the source before copying it. If a rename replaces a long inline name with a shorter one in between, the copy can include stale slab bytes after the new NUL. The subsequent padding starts at the old length, leaving those bytes in task->comm. An unprivileged task can observe the suffix through a count-only syscall tracepoint filter such as COMM ~ "*pattern*". Take a dentry name snapshot before setting comm and release it afterwards. The snapshot retries concurrent renames and either copies the inline name or holds a reference to an immutable external name. This gives both the tracepoint and the length/copy sequence a stable source while preserving the selected executable and the existing comm truncation and padding. Fixes: 543841d18060 ("exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case") Cc: stable@vger.kernel.org Assisted-by: Codex:gpt-6-astra Signed-off-by: Kyle Zeng --- fs/exec.c | 17 +++++++---------- 1 file changed, 7 insertions(+), 10 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 819643408e6d..34cf557a17f7 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1279,19 +1279,16 @@ int begin_new_exec(struct linux_binprm * bprm) */ if (bprm->comm_from_dentry) { struct file *comm_file = bprm_identity_file(bprm); + struct name_snapshot name; /* - * Hold RCU lock to keep the name from being freed behind our back. - * Use acquire semantics to make sure the terminating NUL from - * __d_alloc() is seen. - * - * Note, we're deliberately sloppy here. We don't need to care about - * detecting a concurrent rename and just want a terminated name. + * __set_task_comm() measures the name before copying it. Keep + * a rename from shortening the name and exposing stale bytes + * in the inline name buffer. */ - rcu_read_lock(); - __set_task_comm(me, smp_load_acquire(&comm_file->f_path.dentry->d_name.name), - true); - rcu_read_unlock(); + take_dentry_name_snapshot(&name, comm_file->f_path.dentry); + __set_task_comm(me, name.name.name, true); + release_dentry_name_snapshot(&name); } else { __set_task_comm(me, kbasename(bprm->filename), true); } base-commit: fd179f8a05be3ccae366b9b96e176b51fbe54aab -- 2.53.0