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Thu, 14 May 2026 19:05:10 -0700 (PDT) Received: from v4bel ([58.123.110.97]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-83f19f61e5dsm4134946b3a.51.2026.05.14.19.05.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 May 2026 19:05:10 -0700 (PDT) Date: Fri, 15 May 2026 11:05:06 +0900 From: Hyunwoo Kim To: oleg@redhat.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, torvalds@linux-foundation.org, qsa@qualys.com, kees@kernel.org Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, imv4bel@gmail.com Subject: [PATCH v2] exec: mirror set_dumpable() to thread-group siblings' user_dumpable Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Queue-Id: E528740003 X-Rspamd-Server: rspam04 X-Stat-Signature: uoneet33ud17unrtxmmjhsio7yj6wcz1 X-HE-Tag: 1778810711-958061 X-HE-Meta: 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 3mgy/Tzh zYo+XcOyOl2yMQa7/u1RYHjxYFBaWlwBpqb5Ke7ZLwpzBI8kkjiFA5NFsWe3iiuD1NWNzljXBl+6sPtp+YjwiLPGApJ6nWkFel+3qDRL9aA12zDqT0jCPuDIjCupVCuCHDAN80hWFkyWO4LUF1CNGlGE5LrT69LLGS67BGEdWnfzeONTmjZdDrv11DnuUoWQN8xDfkg9NmWFHhrif/8jXtYQSlaIKigIC4Xx01aFjf55IDkDev5kRHKtSBWBgpI9RAl+ceYVcR23Y1NnbQ5tkkcW/UKIr77UALdJWS9ZajtUk6SuAPbQ+MoRKkAsxO1sWi3bQSCydmucdNTtBgLlDwmi8/deQ+9MQdLP0o+HVBG8vv+DCehBfEJO6A3KEMxsLiJcpX2gg44GpeNQscrnxrqEDv1tqux/MnS8FMVSB6PoRVLwBmeyzT9qMhcNuTG/vVnS8V/6eG5iG0Cyh5UDbVwWjkbm99CUTmePMX9PWwqiIronzYaJ5BouL2E0uOnOPTx8D0CoEihVASps= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: task_still_dumpable() reads task->user_dumpable when task->mm is NULL. That cache is written exactly once in exit_mm(): a single get_dumpable(mm) load taken just before task->mm is cleared. The load is not ordered against set_dumpable() writes performed by CLONE_VM siblings, either via commit_creds() (an euid/egid/fsuid/fsgid change or a capability gain - !cred_cap_issubset(old, new)) or via prctl(PR_SET_DUMPABLE). If a sibling stores SUID_DUMP_DISABLE after the exiting thread observed SUID_DUMP_USER, the live shared mm and the cached value diverge with no later refresh, so task_still_dumpable() keeps returning SUID_DUMP_USER for the exiting task. In set_dumpable(), after the atomic update to mm->flags, walk every thread in current's thread group under rcu_read_lock() and mirror the new SUID_DUMP_USER bit into each task's user_dumpable cache. All in-tree callers of set_dumpable() pass current->mm (commit_creds(), prctl(PR_SET_DUMPABLE), begin_new_exec()), so for_each_thread(current) covers exactly the CLONE_VM thread group whose mm was just updated. The mirror takes task_lock(t) around each per-task write to serialize with exit_mm()'s own user_dumpable RMW: the bit-field shares a word with neighbor fields, and without serialization a race-window expansion between the mirror's store and exit_mm()'s store on the same word can lose the mirror's update. This keeps the cache in sync with the latest set_dumpable() result even after every thread in the group has passed exit_mm(). Fixes: 31e62c2ebbfd ("ptrace: slightly saner 'get_dumpable()' logic") Signed-off-by: Hyunwoo Kim --- Changes in v2: - Move the update from a read-side sibling walk in task_still_dumpable() to a write-side mirror in set_dumpable(); v1 left the cache stale when no live sibling mm remained. - v1: https://lore.kernel.org/all/agZjJdaIGCvf0z_1@v4bel/ --- fs/exec.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index ba12b4c466f6..9732b38b727f 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1910,10 +1910,26 @@ EXPORT_SYMBOL(set_binfmt); */ void set_dumpable(struct mm_struct *mm, int value) { + struct task_struct *t; + bool user; + if (WARN_ON((unsigned)value > SUID_DUMP_ROOT)) return; __mm_flags_set_mask_dumpable(mm, value); + + /* + * Mirror to every sibling's user_dumpable cache, serialized with + * exit_mm()'s write via task_lock(t) to avoid bit-field RMW races. + */ + user = (value == SUID_DUMP_USER); + rcu_read_lock(); + for_each_thread(current, t) { + task_lock(t); + t->user_dumpable = user; + task_unlock(t); + } + rcu_read_unlock(); } static inline struct user_arg_ptr native_arg(const char __user *const __user *p) -- 2.43.0