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b=N20eoL1Jsgw5XjfuLI6ZsoOwg9eChhiIgsCcJTqwwHOYufH6Vm2Iacejx7KD+UhJM hp+jY9uvpH78UD+qN/dq2USZK1tcDkia2izNK7k7iHmCW5loorNNO4SRy5llLN+3Ss k78JqOEnQowNxoXfxaN0E1HyVUysDSKDexIjKrgyPNet3RQ7YL3JJ4qTRcaF4sOPGv xGAzyM2C1kt/uRVL7jx7bHHgt+l/6s/6SzvmN9Klj5ytai1z5Mm0T6OTuTUWLK93xJ juuS4p6fjIXUy2GpTFGrF/r8hzCXGU3TVuvWuAuLyjo3+GfrlxzpomIMxzTfUkpufw xgwag8HbvHC6Q== From: Christian Brauner Date: Fri, 10 Jul 2026 00:30:13 +0200 Subject: [PATCH v2 18/23] binfmt_misc: use a flexible array member for the register string MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260710-work-binfmt_misc-locking-v2-18-2a1c3d4126a7@kernel.org> References: <20260710-work-binfmt_misc-locking-v2-0-2a1c3d4126a7@kernel.org> In-Reply-To: <20260710-work-binfmt_misc-locking-v2-0-2a1c3d4126a7@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: Alexander Viro , Christian Brauner , Jan Kara , linux-mm@kvack.org, Farid Zakaria , jannh@google.com X-Mailer: b4 0.16-dev-4217c X-Developer-Signature: v=1; a=openpgp-sha256; l=2427; i=brauner@kernel.org; h=from:subject:message-id; bh=gAz94TTaskV/1L0+/Cg5xweBbJSb5hGJ0x6PTB2vSzs=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWQFKHx7d2lufmHJzjVTOPenMlpP/KIw9aA9U8W3uZ9aC yxLZ2590FHKwiDGxSArpsji0G4SLrecp2KzUaYGzBxWJpAhDFycAjAR5dcM/6t+rVi3b4vTv/Nf d5qnM4fsVwur4vRYspHzdkPf6UVqRnYM/7NcNbMObtyx0inmzNm9brHHrrpvDVjq/vLvtcMq2oq qxawA X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: B6E08140002 X-Stat-Signature: ufnsmeari1wh3q861836bffrmr4nzhcx X-HE-Tag: 1783636252-511342 X-HE-Meta: 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 f/9Dha1l IDXiIf5eGlRfw75RqVe0t3KVGhUHCfTeX1U6WT12ig42nye2UMudbH293/LvnKxj6SBeNpGAVy/7EB0Ub00drqGmdT1RC+wfOaTYiEroqBEOtqFGsP5TIoEcEeT6yzZoJHJwxgBHbQfbcNUhRzbegtISYGqMNhLBFL/F2P46ROnoxdTTeu1cTWlGysCIK0aAgL6yASUG5J39RAAf3Z0Bw+QQRJ4IJ09QFap17CgmLTyHj/XmPmJ34rke1dmwGEAOjsaW2NFh6VMZNkPrYR8vUgpTJ3x/0yJk3FTPbVAXtm06c1fI8qQmZBiF5SgG6cG8fWBWR6hVMcw/V4qeVlLr0ezUpEBo9kTmsfibVmEA+1W8WhB8= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: create_entry() allocates the entry and the register string it parses into in one chunk and finds the string part again through manual pointer arithmetic behind a cast. Make the layout explicit with a flexible array member and struct_size(), and give the magic pad of trailing delimiters a name while at it. No functional change. Signed-off-by: Christian Brauner (Amutable) --- fs/binfmt_misc.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index 1536e398aa67..c7435d103629 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -59,6 +59,7 @@ struct binfmt_misc_entry { struct file *interp_file; refcount_t users; /* sync removal with load_misc_binary() */ struct rcu_head rcu; + char buf[]; /* register string, fields point in here */ }; static struct file_system_type bm_fs_type; @@ -78,6 +79,9 @@ static struct file_system_type bm_fs_type; */ #define MAX_REGISTER_LENGTH 1920 +/* Trailing delimiter pad so field parsing always terminates at a delimiter. */ +#define MISC_DELIM_PAD 8 + /* Check if @e's magic matches @bprm's buffer, applying the mask if set. */ static bool entry_matches_magic(const struct binfmt_misc_entry *e, const struct linux_binprm *bprm) @@ -345,9 +349,9 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer, size_t count) { struct binfmt_misc_entry *e; - int memsize, err; char *buf, *p; char del; + int err; pr_debug("register: received %zu bytes\n", count); @@ -357,12 +361,12 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer, goto out; err = -ENOMEM; - memsize = sizeof(*e) + count + 8; - e = kmalloc(memsize, GFP_KERNEL_ACCOUNT); + e = kmalloc(struct_size(e, buf, count + MISC_DELIM_PAD), + GFP_KERNEL_ACCOUNT); if (!e) goto out; - p = buf = (char *)e + sizeof(*e); + p = buf = e->buf; memset(e, 0, sizeof(*e)); if (copy_from_user(buf, buffer, count)) @@ -373,7 +377,7 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer, pr_debug("register: delim: %#x {%c}\n", del, del); /* Pad the buffer with the delim to simplify parsing below. */ - memset(buf + count, del, 8); + memset(buf + count, del, MISC_DELIM_PAD); /* Parse the 'name' field. */ e->name = p; -- 2.53.0