From f98d6db17e0a4ca5aebdc36ec9c321733f4aa3d8 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 10 Jul 2026 11:33:21 +0200 Subject: [PATCH] binfmt_misc: split the field parsing out of create_entry() create_entry() is a two hundred line parser with the M and E field handling inlined as the two arms of its largest branch. Move them into parse_magic_fields() and parse_extension_fields() which return the new parse position or NULL so create_entry() itself reads like the register string grammar again. The offset parsing loses a provably dead check on the way: after *s = '\0' and p = s the subsequent if (*p++) always reads the just written NUL byte and can never fail, it only obscured that the code simply advances past the delimiter. With the field parsing gone every remaining failure unwinds the same way, so hand the entry to __free(kfree), return errors directly and pass ownership out via no_free_ptr() on success instead of routing every exit through goto tails. Link: https://patch.msgid.link/20260710-work-binfmt_misc-locking-v3-20-a162f7cb58d6@kernel.org Signed-off-by: Christian Brauner (Amutable) --- fs/binfmt_misc.c | 225 +++++++++++++++++++++++------------------------ 1 file changed, 108 insertions(+), 117 deletions(-) diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index 30a10514cf94..161d7202d895 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -339,6 +339,95 @@ static char *check_special_flags(char *p, struct binfmt_misc_entry *e) } } +/* Parse the 'offset', 'magic' and 'mask' fields of an 'M' entry. */ +static char *parse_magic_fields(struct binfmt_misc_entry *e, char *p, char del) +{ + char *s; + + /* Parse the 'offset' field. */ + s = strchr(p, del); + if (!s) + return NULL; + *s = '\0'; + if (p != s) { + if (kstrtoint(p, 10, &e->offset) || e->offset < 0) + return NULL; + } + p = s + 1; + pr_debug("register: offset: %#x\n", e->offset); + + /* Parse the 'magic' field. */ + e->magic = p; + p = scanarg(p, del); + if (!p || !e->magic[0]) + return NULL; + print_hex_dump_debug( + KBUILD_MODNAME ": register: magic[raw]: ", + DUMP_PREFIX_NONE, 16, 1, e->magic, p - e->magic, true); + + /* Parse the 'mask' field. */ + e->mask = p; + p = scanarg(p, del); + if (!p) + return NULL; + if (!e->mask[0]) { + e->mask = NULL; + pr_debug("register: mask[raw]: none\n"); + } else { + print_hex_dump_debug( + KBUILD_MODNAME ": register: mask[raw]: ", + DUMP_PREFIX_NONE, 16, 1, e->mask, p - e->mask, true); + } + + /* + * Decode the magic & mask fields. Note: while we might have accepted + * embedded NUL bytes from above, the unescape helpers will stop at + * the first one they encounter. + */ + e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX); + if (e->mask && string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size) + return NULL; + if (e->size > BINPRM_BUF_SIZE || BINPRM_BUF_SIZE - e->size < e->offset) + return NULL; + pr_debug("register: magic/mask length: %i\n", e->size); + print_hex_dump_debug( + KBUILD_MODNAME ": register: magic[decoded]: ", + DUMP_PREFIX_NONE, 16, 1, e->magic, e->size, true); + if (e->mask) + print_hex_dump_debug( + KBUILD_MODNAME ": register: mask[decoded]: ", + DUMP_PREFIX_NONE, 16, 1, e->mask, e->size, true); + return p; +} + +/* Parse the 'magic' field of an 'E' entry: the filename extension. */ +static char *parse_extension_fields(struct binfmt_misc_entry *e, char *p, + char del) +{ + /* Skip the 'offset' field. */ + p = strchr(p, del); + if (!p) + return NULL; + *p++ = '\0'; + + /* Parse the 'magic' field. */ + e->magic = p; + p = strchr(p, del); + if (!p) + return NULL; + *p++ = '\0'; + if (!e->magic[0] || strchr(e->magic, '/')) + return NULL; + pr_debug("register: extension: {%s}\n", e->magic); + + /* Skip the 'mask' field. */ + p = strchr(p, del); + if (!p) + return NULL; + *p++ = '\0'; + return p; +} + /* * This registers a new binary format, it recognises the syntax * ':name:type:offset:magic:mask:interpreter:flags' @@ -347,29 +436,26 @@ static char *check_special_flags(char *p, struct binfmt_misc_entry *e) static struct binfmt_misc_entry *create_entry(const char __user *buffer, size_t count) { - struct binfmt_misc_entry *e; + struct binfmt_misc_entry *e __free(kfree) = NULL; char *buf, *p; char del; - int err; pr_debug("register: received %zu bytes\n", count); /* some sanity checks */ - err = -EINVAL; if ((count < 11) || (count > MAX_REGISTER_LENGTH)) - goto out; + return ERR_PTR(-EINVAL); - err = -ENOMEM; e = kmalloc(struct_size(e, buf, count + MISC_DELIM_PAD), GFP_KERNEL_ACCOUNT); if (!e) - goto out; + return ERR_PTR(-ENOMEM); p = buf = e->buf; memset(e, 0, sizeof(*e)); if (copy_from_user(buf, buffer, count)) - goto efault; + return ERR_PTR(-EFAULT); del = *p++; /* delimeter */ @@ -377,7 +463,7 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer, /* A flag-char delimiter runs the flag scan off the buffer. */ if (del == 'P' || del == 'O' || del == 'C' || del == 'F') - goto einval; + return ERR_PTR(-EINVAL); /* Pad the buffer with the delim to simplify parsing below. */ memset(buf + count, del, MISC_DELIM_PAD); @@ -386,13 +472,13 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer, e->name = p; p = strchr(p, del); if (!p) - goto einval; + return ERR_PTR(-EINVAL); *p++ = '\0'; if (!e->name[0] || !strcmp(e->name, ".") || !strcmp(e->name, "..") || strchr(e->name, '/')) - goto einval; + return ERR_PTR(-EINVAL); pr_debug("register: name: {%s}\n", e->name); @@ -407,111 +493,26 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer, e->flags = BIT(MISC_FMT_ENABLED_BIT) | BIT(MISC_FMT_MAGIC_BIT); break; default: - goto einval; + return ERR_PTR(-EINVAL); } if (*p++ != del) - goto einval; + return ERR_PTR(-EINVAL); - if (test_bit(MISC_FMT_MAGIC_BIT, &e->flags)) { - /* Handle the 'M' (magic) format. */ - char *s; - - /* Parse the 'offset' field. */ - s = strchr(p, del); - if (!s) - goto einval; - *s = '\0'; - if (p != s) { - int r = kstrtoint(p, 10, &e->offset); - if (r != 0 || e->offset < 0) - goto einval; - } - p = s; - if (*p++) - goto einval; - pr_debug("register: offset: %#x\n", e->offset); - - /* Parse the 'magic' field. */ - e->magic = p; - p = scanarg(p, del); - if (!p) - goto einval; - if (!e->magic[0]) - goto einval; - print_hex_dump_debug( - KBUILD_MODNAME ": register: magic[raw]: ", - DUMP_PREFIX_NONE, 16, 1, e->magic, p - e->magic, true); - - /* Parse the 'mask' field. */ - e->mask = p; - p = scanarg(p, del); - if (!p) - goto einval; - if (!e->mask[0]) { - e->mask = NULL; - pr_debug("register: mask[raw]: none\n"); - } else { - print_hex_dump_debug( - KBUILD_MODNAME ": register: mask[raw]: ", - DUMP_PREFIX_NONE, 16, 1, e->mask, p - e->mask, - true); - } - - /* - * Decode the magic & mask fields. - * Note: while we might have accepted embedded NUL bytes from - * above, the unescape helpers here will stop at the first one - * it encounters. - */ - e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX); - if (e->mask && - string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size) - goto einval; - if (e->size > BINPRM_BUF_SIZE || - BINPRM_BUF_SIZE - e->size < e->offset) - goto einval; - pr_debug("register: magic/mask length: %i\n", e->size); - print_hex_dump_debug( - KBUILD_MODNAME ": register: magic[decoded]: ", - DUMP_PREFIX_NONE, 16, 1, e->magic, e->size, true); - if (e->mask) - print_hex_dump_debug( - KBUILD_MODNAME ": register: mask[decoded]: ", - DUMP_PREFIX_NONE, 16, 1, e->mask, e->size, true); - } else { - /* Handle the 'E' (extension) format. */ - - /* Skip the 'offset' field. */ - p = strchr(p, del); - if (!p) - goto einval; - *p++ = '\0'; - - /* Parse the 'magic' field. */ - e->magic = p; - p = strchr(p, del); - if (!p) - goto einval; - *p++ = '\0'; - if (!e->magic[0] || strchr(e->magic, '/')) - goto einval; - pr_debug("register: extension: {%s}\n", e->magic); - - /* Skip the 'mask' field. */ - p = strchr(p, del); - if (!p) - goto einval; - *p++ = '\0'; - } + if (test_bit(MISC_FMT_MAGIC_BIT, &e->flags)) + p = parse_magic_fields(e, p, del); + else + p = parse_extension_fields(e, p, del); + if (!p) + return ERR_PTR(-EINVAL); /* Parse the 'interpreter' field. */ e->interpreter = p; p = strchr(p, del); if (!p) - goto einval; + return ERR_PTR(-EINVAL); *p++ = '\0'; if (!e->interpreter[0]) - goto einval; + return ERR_PTR(-EINVAL); pr_debug("register: interpreter: {%s}\n", e->interpreter); /* Parse the 'flags' field. */ @@ -519,19 +520,9 @@ static struct binfmt_misc_entry *create_entry(const char __user *buffer, if (*p == '\n') p++; if (p != buf + count) - goto einval; + return ERR_PTR(-EINVAL); - return e; - -out: - return ERR_PTR(err); - -efault: - kfree(e); - return ERR_PTR(-EFAULT); -einval: - kfree(e); - return ERR_PTR(-EINVAL); + return no_free_ptr(e); } /* Commands accepted by the /status and / files. */