exfat: fix improper check of dentry.stream.valid_size

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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 <kkamagui@gmail.com>
Signed-off-by: Seunghun Han <kkamagui@gmail.com>
Co-developed-by: Jihoon Kwon <jimmyxyz010315@gmail.com>
Signed-off-by: Jihoon Kwon <jimmyxyz010315@gmail.com>
Signed-off-by: Jaehun Gou <p22gone@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

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Jaehun Gou 2025-10-14 22:01:46 +09:00 • committed by Namjae Jeon

parent 9b332cece9

commit 82ebecdc74

1 changed files with 5 additions and 1 deletions

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fs/exfat/namei.c

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