In exfat_nls_to_ucs2(), if there is no NLS loss and the char-to-ucs2 conversion is successfully completed, the variable "i" will have the same value as len.
However, exfat_nls_to_ucs2() checks p_cstring[i] to determine whether nls is lost immediately after the while loop ends, so if len is FSLABEL_MAX, "i" will also be FSLABEL_MAX immediately after the while loop ends, resulting in an out-of-bounds read of 1 byte from the p_cstring stack memory.
Therefore, to prevent this and properly determine whether nls has been lost, it should be modified to check if "i" and len are equal, rather than dereferencing p_cstring.
Cc: stable@vger.kernel.org Reported-by: syzbot+98cc76a76de46b3714d4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=98cc76a76de46b3714d4 Fixes: 370e812b3ec1 ("exfat: add nls operations") Signed-off-by: Jeongjun Park aha310510@gmail.com --- fs/exfat/nls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/exfat/nls.c b/fs/exfat/nls.c index 8243d94ceaf4..de06abe426d7 100644 --- a/fs/exfat/nls.c +++ b/fs/exfat/nls.c @@ -616,7 +616,7 @@ static int exfat_nls_to_ucs2(struct super_block *sb, unilen++; }
- if (p_cstring[i] != '\0') + if (i != len) lossy |= NLS_NAME_OVERLEN;
*uniname = '\0'; --
On Friday 10 October 2025 14:03:29 Jeongjun Park wrote:
In exfat_nls_to_ucs2(), if there is no NLS loss and the char-to-ucs2 conversion is successfully completed, the variable "i" will have the same value as len.
However, exfat_nls_to_ucs2() checks p_cstring[i] to determine whether nls is lost immediately after the while loop ends, so if len is FSLABEL_MAX, "i" will also be FSLABEL_MAX immediately after the while loop ends, resulting in an out-of-bounds read of 1 byte from the p_cstring stack memory.
Therefore, to prevent this and properly determine whether nls has been lost, it should be modified to check if "i" and len are equal, rather than dereferencing p_cstring.
Cc: stable@vger.kernel.org Reported-by: syzbot+98cc76a76de46b3714d4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=98cc76a76de46b3714d4 Fixes: 370e812b3ec1 ("exfat: add nls operations") Signed-off-by: Jeongjun Park aha310510@gmail.com
fs/exfat/nls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/exfat/nls.c b/fs/exfat/nls.c index 8243d94ceaf4..de06abe426d7 100644 --- a/fs/exfat/nls.c +++ b/fs/exfat/nls.c @@ -616,7 +616,7 @@ static int exfat_nls_to_ucs2(struct super_block *sb, unilen++; }
- if (p_cstring[i] != '\0')
- if (i != len) lossy |= NLS_NAME_OVERLEN;
*uniname = '\0';
Looks good for me,
Reviewed-by: Pali Rohár pali@kernel.org
On Fri, Oct 10, 2025 at 2:04 PM Jeongjun Park aha310510@gmail.com wrote:
In exfat_nls_to_ucs2(), if there is no NLS loss and the char-to-ucs2 conversion is successfully completed, the variable "i" will have the same value as len.
However, exfat_nls_to_ucs2() checks p_cstring[i] to determine whether nls is lost immediately after the while loop ends, so if len is FSLABEL_MAX, "i" will also be FSLABEL_MAX immediately after the while loop ends, resulting in an out-of-bounds read of 1 byte from the p_cstring stack memory.
Therefore, to prevent this and properly determine whether nls has been lost, it should be modified to check if "i" and len are equal, rather than dereferencing p_cstring.
Cc: stable@vger.kernel.org Reported-by: syzbot+98cc76a76de46b3714d4@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=98cc76a76de46b3714d4 Fixes: 370e812b3ec1 ("exfat: add nls operations") Signed-off-by: Jeongjun Park aha310510@gmail.com
fs/exfat/nls.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/exfat/nls.c b/fs/exfat/nls.c index 8243d94ceaf4..de06abe426d7 100644 --- a/fs/exfat/nls.c +++ b/fs/exfat/nls.c @@ -616,7 +616,7 @@ static int exfat_nls_to_ucs2(struct super_block *sb, unilen++; }
if (p_cstring[i] != '\0')
if (i != len) lossy |= NLS_NAME_OVERLEN;
As I said before, the core problem is passing an incorrect length in the ioctl FS_IOC_SETFSLABEL call. While your change may fix the symptom, it doesn't fix the root cause. Furthermore, NLS_NAME_OVERLEN macro is unnecessary. That will result in different errors when creating a file with trailing periods with utf8 and the other iocharset. Please remove it and make the same error handling for maximum length consistent with exfat_utf8_to_utf16().
*uniname = '\0';--
linux-stable-mirror@lists.linaro.org
-
Jeongjun Park -
Namjae Jeon -
Pali Rohár