jfs_readdir() converts each on-disk name into a struct jfs_dirent in a PAGE_SIZE buffer, and stops filling the buffer when the next entry might not fit: if (((long) jfs_dirent + d->namlen + 1) > ((long)dirent_buf + PAGE_SIZE)) { That check undercounts twice. The name is written at jfs_dirent->name, after the 14-byte header, not at jfs_dirent. And d->namlen counts UCS-2 characters, while jfs_strfromUCS_le() lets the codepage's uni2char() write up to NLS_MAX_CHARSET_SIZE bytes for each one; with iocharset=utf8 most non-ASCII characters take two or three bytes. So an entry that passes the check can still be written past the end of the buffer. Since commit de9f4f0b2c0f ("jfs: replace __get_free_page() with kmalloc()") the buffer comes from kmalloc-4k and KASAN reports it: BUG: KASAN: slab-out-of-bounds in utf32_to_utf8+0x24d/0x3d0 fs/nls/nls_base.c:111 Write of size 1 at addr ffff888039ad7000 by task syz-executor304/5946 utf32_to_utf8+0x24d/0x3d0 fs/nls/nls_base.c:111 uni2char+0x35/0xa0 fs/nls/nls_utf8.c:21 jfs_strfromUCS_le+0xd2/0x3d0 fs/jfs/jfs_unicode.c:31 jfs_readdir+0x16fd/0x33f0 fs/jfs/jfs_dtree.c:2984 The buggy address is located 0 bytes to the right of allocated 4096-byte region [ffff888039ad6000, ffff888039ad7000) Before that commit the same write went into whatever page followed. Check against the worst case instead: the name starts at jfs_dirent->name and each character can take NLS_MAX_CHARSET_SIZE bytes, or one byte when no codepage is set. The largest entry is then 255 * 6 + 15 bytes, so an empty buffer still always takes at least one entry and readdir keeps making progress. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+a2748ba908c108e7e525@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Yogesh Gaur --- Built with W=1 only; not runtime-tested. fs/jfs/jfs_dtree.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c index 8ce6e4458cc2..d930e577a496 100644 --- a/fs/jfs/jfs_dtree.c +++ b/fs/jfs/jfs_dtree.c @@ -2712,6 +2712,8 @@ int jfs_readdir(struct file *file, struct dir_context *ctx) { struct inode *ip = file_inode(file); struct nls_table *codepage = JFS_SBI(ip->i_sb)->nls_tab; + /* most bytes one on-disk character can turn into in jfs_dirent */ + int max_charlen = codepage ? NLS_MAX_CHARSET_SIZE : 1; int rc = 0; loff_t dtpos; /* legacy OS/2 style position */ struct dtoffset { @@ -2910,9 +2912,10 @@ int jfs_readdir(struct file *file, struct dir_context *ctx) d = (struct ldtentry *) & p->slot[stbl[i]]; - if (((long) jfs_dirent + d->namlen + 1) > + if (((long)jfs_dirent->name + + d->namlen * max_charlen + 1) > ((long)dirent_buf + PAGE_SIZE)) { - /* DBCS codepages could overrun dirent_buf */ + /* the converted name might not fit */ index = i; overflow = 1; break; -- 2.55.0.windows.5