ocfs2: fix readdir position truncation on 32-bit kernels

Overview

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

ocfs2: fix readdir position truncation on 32-bit kernels

In ocfs2_dir_foreach_blk_el(), the directory cookie position is rebuilt with

ctx->pos = (ctx->pos & ~(sb->s_blocksize - 1)) | offset;

ctx->pos is loff_t (signed 64-bit), while sb->s_blocksize is unsigned long. On 32-bit kernels unsigned long is 32-bit, so the mask

~(sb->s_blocksize - 1)

is computed as a 32-bit unsigned value (e.g. 0xfffff000 for a 4 KiB block size). In the AND expression with the 64-bit ctx->pos, that unsigned operand is zero-extended to 64 bits per the usual arithmetic conversions, yielding 0x00000000fffff000. The high 32 bits of ctx->pos are silently cleared, even though directory size is allowed to exceed 4 GiB.

When readdir() crosses the 4 GiB boundary on a 32-bit kernel the position is reset back into the first 4 GiB block, making the re-validation path re-enumerate already-returned dirents indefinitely.

This is ocfs2_dir_foreach_blk_el(), the extent-list readdir path taken for all non-inline directories, so a directory large enough to cross 4 GiB reaches it.

This is the same class of bug that commit 3dce5bb82c97 ("exfat: Fix bitwise operation having different size") fixed in exfat, and the fix mirrors the equivalent ext4 fix in this series. Cast the operand to loff_t so the mask is 64-bit before the AND:

ctx->pos = (ctx->pos & ~((loff_t)sb->s_blocksize - 1)) | offset;

64-bit kernels are unaffected.

Affected

• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < c28dc3407937aa8f225942538cd585c9b28ea65a
• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < 94569154ba49f5f85645d2019c8e206213d8404e
• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < 1ae7029823ae4c91664cb32eec7fb8dd5e1a337a
• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < f9dd5cad8d09110ddff2db1fe756aae93c7552ff
• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < 1001fb3b69a11eaa0dc7c7428f6edfa48b88997a
• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < c0c165487a2ea5a37ddcdab4259157b7a527129c
• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < b53e2b271eeb6040c2a4a78230c570dc41cdcfa4
• Linux >= ccd979bdbce9fba8412beb3f1de68a9d0171b12c < a63308ab426f3a3c7e33b02c150ea59054620261
• Linux 2.6.16

Remediation

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