From 0c52750caaaccee8b0e929450fe6538ec4985722 Mon Sep 17 00:00:00 2001 From: Matthias Goergens Date: Fri, 30 Oct 2026 22:05:36 +0800 Subject: [PATCH] udf: fix preallocation discarding before an empty allocation extent udf_discard_prealloc() finds the last extent of a file by peeking at the next one with udf_next_aext() and stopping when that returns 0. The peek reads into eloc and elen, and the code then uses them as the last extent. But when udf_next_aext() returns 0 they hold no defined value: if the extent list ends in a continuation descriptor that leads to an empty allocation extent, they describe that continuation, i.e. the block of the empty allocation extent, one block long. The kernel creates such lists itself: when udf_delete_aext() removes the only descriptor of the last allocation extent in a list, it leaves that allocation extent empty and the continuation to it in place. If the last extent is a preallocation, udf_discard_prealloc() deletes it with udf_delete_aext(), which finds the following allocation extent empty, so it also removes the continuation and frees that allocation extent's block. udf_discard_prealloc() then frees eloc and elen: that block a second time, instead of the preallocated blocks. On a space bitmap the preallocated blocks leak and the free block count drifts. On an unallocated space table the second free adds a second free extent for the same block, which is later handed out twice: fsx as run by generic/091 and generic/263 ends up with two parts of its test file in one block and reads back bad data. Peek into separate variables, so that eloc and elen keep the last extent that udf_next_aext() returned with 1. Fixes: cfe4c1b25dd6 ("udf: Fix preallocation discarding at indirect extent boundary") Cc: stable@vger.kernel.org Suggested-by: Jan Kara Signed-off-by: Matthias Goergens Link: https://patch.msgid.link/480eccd1264a4cea5226fc36ed108931b2c403fb.1793349907.git.matthias.goergens@gmail.com Signed-off-by: Jan Kara --- fs/udf/truncate.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/fs/udf/truncate.c b/fs/udf/truncate.c index 0990f94b8551..75151a59f0da 100644 --- a/fs/udf/truncate.c +++ b/fs/udf/truncate.c @@ -124,8 +124,8 @@ void udf_discard_prealloc(struct inode *inode) { struct extent_position epos = {}; struct extent_position prev_epos = {}; - struct kernel_lb_addr eloc; - uint32_t elen; + struct kernel_lb_addr eloc, tmpeloc; + uint32_t elen, tmpelen; uint64_t lbcount = 0; int8_t etype = -1; struct udf_inode_info *iinfo = UDF_I(inode); @@ -141,7 +141,8 @@ void udf_discard_prealloc(struct inode *inode) /* Find the last extent in the file */ while (1) { - ret = udf_next_aext(inode, &epos, &eloc, &elen, &tmpetype, 0); + ret = udf_next_aext(inode, &epos, &tmpeloc, &tmpelen, + &tmpetype, 0); if (ret < 0) goto out; if (ret == 0)