From 351817226fbf0031c4c63d1f5d7f15c3172312eb Mon Sep 17 00:00:00 2001 From: Yuejie Shi Date: Mon, 3 Aug 2026 12:34:32 +0800 Subject: [PATCH] fs/ntfs3: validate the EA value length in ntfs_read_ea() ntfs_read_ea() checks the $EA list for consistency, but it only recomputes the packed size of an entry when the entry's own size field is zero: for (off = 0; off < size; off += ea_size) { const struct EA_FULL *ef = Add2Ptr(ea_p, off); u32 bytes = size - off; ... if (ef->size) { ea_size = le32_to_cpu(ef->size); if (ea_size > bytes) goto out1; continue; /* <- elength never checked */ } ... ea_size = ALIGN(struct_size(ef, name, 1 + ef->name_len + le16_to_cpu(ef->elength)), 4); if (ea_size > bytes) goto out1; } ef->size is non-zero for every entry except the last one, and it is what ntfs3 itself writes (ntfs_set_ea() stores exactly that aligned packed size), so in practice elength is not validated at all. find_ea() then uses unpacked_ea_size(), which also prefers ea->size when it is set, so it agrees and hands the entry back. ntfs_get_ea() copies elength bytes with no further bound of its own: len = le16_to_cpu(ea->elength); ... if (len > size) { /* size is the *caller's* buffer */ err = -ERANGE; ... } memcpy(buffer, ea->name + ea->name_len + 1, len); so a caller that supplies a large enough buffer receives up to 64 KiB of whatever follows the small $EA allocation -- straight to userspace via getxattr(2). Compute the packed size unconditionally and require it to fit in the entry. Hoist the "bytes < offsetof(struct EA_FULL, name)" test above the ef->size branch as well: name_len and elength were being read there without it, which is itself a small over-read of the kmalloc'd buffer when fewer than 8 bytes are left. The old "bytes < sizeof(ef->size)" test is subsumed by it. # mkntfs image; create /mnt/ntfs/poc with user.ntfs6 set, then rewrite # that EA_FULL's elength from 0xf to 0xff00 on the raw device mount -t ntfs3 -o ro /dev/vda /mnt/ntfs getxattr("/mnt/ntfs/poc", "user.ntfs6", buf, 128 * 1024); BUG: KASAN: slab-out-of-bounds in ntfs_get_ea+0x294/0x3e0 Read of size 65280 at addr ffff0000cca53acf by task xattr_probe/142 __asan_memcpy+0x3c/0xa0 ntfs_get_ea+0x294/0x3e0 ntfs_getxattr+0x284/0x318 __vfs_getxattr+0x104/0x160 vfs_getxattr+0x1b4/0x1e0 do_getxattr+0xcc/0x230 path_getxattrat+0x184/0x270 __arm64_sys_getxattr+0x64/0x80 Allocated by task 142: __kmalloc_noprof+0x294/0x668 ntfs_read_ea+0x1e4/0x420 ntfs_get_ea+0x2c8/0x3e0 The buggy address belongs to the object at ffff0000cca53a80 which belongs to the cache kmalloc-96 of size 96 The object being over-read is the one ntfs_read_ea() just allocated, and it is 96 bytes. Entries written by ntfs3 and by Windows set size to the aligned packed size, so the new test does not reject anything a working filesystem produces. Fixes: be71b5cba2e6 ("fs/ntfs3: Add attrib operations") Cc: stable@vger.kernel.org Signed-off-by: Yuejie Shi [almaz.alexandrovich@paragon-software.com: applied as-is, logic is the same but the code is cleaner] Signed-off-by: Konstantin Komarov --- fs/ntfs3/xattr.c | 45 ++++++++++++++------------------------------- 1 file changed, 14 insertions(+), 31 deletions(-) diff --git a/fs/ntfs3/xattr.c b/fs/ntfs3/xattr.c index d6ad06415318..e1fa58aa0361 100644 --- a/fs/ntfs3/xattr.c +++ b/fs/ntfs3/xattr.c @@ -146,49 +146,32 @@ static int ntfs_read_ea(struct ntfs_inode *ni, struct EA_FULL **ea, for (off = 0; off < size; off += ea_size) { const struct EA_FULL *ef = Add2Ptr(ea_p, off); u32 bytes = size - off; - size_t need; - - /* Check if we can use field ea->size. */ - if (bytes < sizeof(ef->size)) - goto out1; + u32 packed_size; /* Check if we can use fields ef->name_len and ef->elength. */ if (bytes < offsetof(struct EA_FULL, name)) goto out1; - /* Size needed to hold this record's name and value. */ - need = struct_size(ef, name, - 1 + ef->name_len + le16_to_cpu(ef->elength)); + /* + * The name and the value have to fit in the entry whether or + * not ef->size is set, because ntfs_get_ea() copies elength + * bytes out of this buffer and checks them only against the + * caller supplied buffer size. + */ + packed_size = + ALIGN(struct_size(ef, name, + 1 + ef->name_len + + le16_to_cpu(ef->elength)), + 4); if (ef->size) { ea_size = le32_to_cpu(ef->size); - /* ef->size must fit the list and cover the record. */ - if (ea_size > bytes || ea_size < need) - goto out1; - if (bytes < offsetof(struct EA_FULL, name)) - goto out1; - - /* Check if we can use fields ef->name_len and ef->elength. */ - if (bytes < offsetof(struct EA_FULL, name)) - goto out1; - - /* - * The declared entry size (ef->size) must be large - * enough to hold the name and value. Otherwise a later - * reader such as ntfs_get_ea() copies ef->elength bytes - * starting past the entry, reading out of bounds of the - * ea buffer and leaking adjacent heap memory to - * userspace via getxattr(). - */ - if (struct_size(ef, name, - 1 + ef->name_len + - le16_to_cpu(ef->elength)) > - ea_size) + if (ea_size > bytes || packed_size > ea_size) goto out1; continue; } - ea_size = ALIGN(need, 4); + ea_size = packed_size; if (ea_size > bytes) goto out1; }