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

Overview

In the Linux kernel, the following vulnerability has been resolved:

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.

Affected

• Linux >= be71b5cba2e6485e8959da7a9f9a44461a1bb074 < 6f07a590616ff5f57f7c041d98e463fad9e9f763
• Linux >= be71b5cba2e6485e8959da7a9f9a44461a1bb074 < a89bc96d5abd8a4a8d5d911884ea347efcdf460b
• Linux >= be71b5cba2e6485e8959da7a9f9a44461a1bb074 < af839013c70a24779f9d1afb1575952009312d38
• Linux >= be71b5cba2e6485e8959da7a9f9a44461a1bb074 < 78b61f7eac37a63284774b147f38dd0be6cad43c
• Linux >= be71b5cba2e6485e8959da7a9f9a44461a1bb074 < c0b43c45d45f59e7faad48675a50231a210c379b
• Linux >= be71b5cba2e6485e8959da7a9f9a44461a1bb074 < 3c3a6e951b9b53dab2ac460a655313cf04c4a10a
• Linux >= be71b5cba2e6485e8959da7a9f9a44461a1bb074 < 4b90f16e4bb5607fb35e7802eb67874038da4640
• Linux 5.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.