fs: ntfs3: fix infinite loop in attr_load_runs_range on inconsistent metadata

We found an infinite loop bug in the ntfs3 file system that can lead to a
Denial-of-Service (DoS) condition.

A malformed NTFS image can cause an infinite loop when an attribute header
indicates an empty run list, while directory entries reference it as
containing actual data. In NTFS, setting evcn=-1 with svcn=0 is a valid way
to represent an empty run list, and run_unpack() correctly handles this by
checking if evcn + 1 equals svcn and returning early without parsing any run
data. However, this creates a problem when there is metadata inconsistency,
where the attribute header claims to be empty (evcn=-1) but the caller
expects to read actual data. When run_unpack() immediately returns success
upon seeing this condition, it leaves the runs_tree uninitialized with
run->runs as a NULL. The calling function attr_load_runs_range() assumes
that a successful return means that the runs were loaded and sets clen to 0,
expecting the next run_lookup_entry() call to succeed. Because runs_tree
remains uninitialized, run_lookup_entry() continues to fail, and the loop
increments vcn by zero (vcn += 0), leading to an infinite loop.

This patch adds a retry counter to detect when run_lookup_entry() fails
consecutively after attr_load_runs_vcn(). If the run is still not found on
the second attempt, it indicates corrupted metadata and returns -EINVAL,
preventing the Denial-of-Service (DoS) vulnerability.

Co-developed-by: Seunghun Han <kkamagui@gmail.com>
Signed-off-by: Seunghun Han <kkamagui@gmail.com>
Co-developed-by: Jihoon Kwon <kjh010315@gmail.com>
Signed-off-by: Jihoon Kwon <kjh010315@gmail.com>
Signed-off-by: Jaehun Gou <p22gone@gmail.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

0 files changed, 0 insertions, 0 deletions