From 82ebecdc74ff555daf70b811d854b1f32a296bea Mon Sep 17 00:00:00 2001 From: Jaehun Gou Date: Tue, 14 Oct 2025 22:01:46 +0900 Subject: [PATCH 1/2] exfat: fix improper check of dentry.stream.valid_size MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit We found an infinite loop bug in the exFAT file system that can lead to a Denial-of-Service (DoS) condition. When a dentry in an exFAT filesystem is malformed, the following system calls — SYS_openat, SYS_ftruncate, and SYS_pwrite64 — can cause the kernel to hang. Root cause analysis shows that the size validation code in exfat_find() does not check whether dentry.stream.valid_size is negative. As a result, the system calls mentioned above can succeed and eventually trigger the DoS issue. This patch adds a check for negative dentry.stream.valid_size to prevent this vulnerability. Co-developed-by: Seunghun Han Signed-off-by: Seunghun Han Co-developed-by: Jihoon Kwon Signed-off-by: Jihoon Kwon Signed-off-by: Jaehun Gou Signed-off-by: Namjae Jeon --- fs/exfat/namei.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c index 7eb9c67fd35f..2364b49f050a 100644 --- a/fs/exfat/namei.c +++ b/fs/exfat/namei.c @@ -642,10 +642,14 @@ static int exfat_find(struct inode *dir, const struct qstr *qname, info->type = exfat_get_entry_type(ep); info->attr = le16_to_cpu(ep->dentry.file.attr); - info->size = le64_to_cpu(ep2->dentry.stream.valid_size); info->valid_size = le64_to_cpu(ep2->dentry.stream.valid_size); info->size = le64_to_cpu(ep2->dentry.stream.size); + if (info->valid_size < 0) { + exfat_fs_error(sb, "data valid size is invalid(%lld)", info->valid_size); + return -EIO; + } + if (unlikely(EXFAT_B_TO_CLU_ROUND_UP(info->size, sbi) > sbi->used_clusters)) { exfat_fs_error(sb, "data size is invalid(%lld)", info->size); return -EIO; From 2d8636119b92970ba135c3c4da87d24dbfdeb8ca Mon Sep 17 00:00:00 2001 From: Jeongjun Park Date: Wed, 15 Oct 2025 16:34:54 +0900 Subject: [PATCH 2/2] exfat: fix out-of-bounds in exfat_nls_to_ucs2() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Since the len argument value passed to exfat_ioctl_set_volume_label() from exfat_nls_to_utf16() is passed 1 too large, an out-of-bounds read occurs when dereferencing p_cstring in exfat_nls_to_ucs2() later. And because of the NLS_NAME_OVERLEN macro, another error occurs when creating a file with a period at the end using utf8 and other iocharsets. So to avoid this, you should remove the code that uses NLS_NAME_OVERLEN macro and make the len argument value be the length of the label string, but with a maximum length of FSLABEL_MAX - 1. Reported-by: syzbot+98cc76a76de46b3714d4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=98cc76a76de46b3714d4 Fixes: d01579d590f7 ("exfat: Add support for FS_IOC_{GET,SET}FSLABEL") Suggested-by: Pali Rohár Signed-off-by: Jeongjun Park Signed-off-by: Namjae Jeon --- fs/exfat/exfat_fs.h | 1 - fs/exfat/file.c | 7 ++++--- fs/exfat/namei.c | 2 +- fs/exfat/nls.c | 3 --- 4 files changed, 5 insertions(+), 8 deletions(-) diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h index 329697c89d09..38210fb6901c 100644 --- a/fs/exfat/exfat_fs.h +++ b/fs/exfat/exfat_fs.h @@ -29,7 +29,6 @@ enum exfat_error_mode { enum { NLS_NAME_NO_LOSSY = 0, /* no lossy */ NLS_NAME_LOSSY = 1 << 0, /* just detected incorrect filename(s) */ - NLS_NAME_OVERLEN = 1 << 1, /* the length is over than its limit */ }; #define EXFAT_HASH_BITS 8 diff --git a/fs/exfat/file.c b/fs/exfat/file.c index f246cf439588..adc37b4d7fc2 100644 --- a/fs/exfat/file.c +++ b/fs/exfat/file.c @@ -509,8 +509,8 @@ static int exfat_ioctl_get_volume_label(struct super_block *sb, unsigned long ar static int exfat_ioctl_set_volume_label(struct super_block *sb, unsigned long arg) { - int ret = 0, lossy; - char label[FSLABEL_MAX]; + int ret = 0, lossy, label_len; + char label[FSLABEL_MAX] = {0}; struct exfat_uni_name uniname; if (!capable(CAP_SYS_ADMIN)) @@ -520,8 +520,9 @@ static int exfat_ioctl_set_volume_label(struct super_block *sb, return -EFAULT; memset(&uniname, 0, sizeof(uniname)); + label_len = strnlen(label, FSLABEL_MAX - 1); if (label[0]) { - ret = exfat_nls_to_utf16(sb, label, FSLABEL_MAX, + ret = exfat_nls_to_utf16(sb, label, label_len, &uniname, &lossy); if (ret < 0) return ret; diff --git a/fs/exfat/namei.c b/fs/exfat/namei.c index 2364b49f050a..745dce29ddb5 100644 --- a/fs/exfat/namei.c +++ b/fs/exfat/namei.c @@ -442,7 +442,7 @@ static int __exfat_resolve_path(struct inode *inode, const unsigned char *path, return namelen; /* return error value */ if ((lossy && !lookup) || !namelen) - return (lossy & NLS_NAME_OVERLEN) ? -ENAMETOOLONG : -EINVAL; + return -EINVAL; return 0; } diff --git a/fs/exfat/nls.c b/fs/exfat/nls.c index 8243d94ceaf4..57db08a5271c 100644 --- a/fs/exfat/nls.c +++ b/fs/exfat/nls.c @@ -616,9 +616,6 @@ static int exfat_nls_to_ucs2(struct super_block *sb, unilen++; } - if (p_cstring[i] != '\0') - lossy |= NLS_NAME_OVERLEN; - *uniname = '\0'; p_uniname->name_len = unilen; p_uniname->name_hash = exfat_calc_chksum16(upname, unilen << 1, 0,