[PATCH 2/2] afs: Fix directory entry size calculation
David Howells
dhowells at redhat.com
Wed Dec 23 08:49:31 EST 2020
The number of dirent records used by an AFS directory entry should be
calculated using the assumption that there is a 16-byte name field in the
first block, rather than a 20-byte name field (which is actually the case).
This miscalculation is historic and effectively standard, so we have to use
it.
The calculation we need to use is:
1 + (((strlen(name) + 1) + 15) >> 5)
where we are adding one to the strlen() result to account for the NUL
termination.
Fix this by the following means:
(1) Create an inline function to do the calculation for a given name
length.
(2) Use the function to calculate the number of records used for a dirent
in afs_dir_iterate_block().
Use this to move the over-end check out of the loop since it only
needs to be done once.
Further use this to only go through the loop for the 2nd+ records
composing an entry. The only test there now is for if the record is
allocated - and we already checked the first block at the top of the
outer loop.
(3) Add a max name length check in afs_dir_iterate_block().
(4) Make afs_edit_dir_add() and afs_edit_dir_remove() use the function
from (1) to calculate the number of blocks rather than doing it
incorrectly themselves.
Fixes: 63a4681ff39c ("afs: Locally edit directory data for mkdir/create/unlink/...")
Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: David Howells <dhowells at redhat.com>
---
fs/afs/dir.c | 49 +++++++++++++++++++++++---------------------
fs/afs/dir_edit.c | 6 ++---
fs/afs/xdr_fs.h | 14 ++++++++++++-
include/trace/events/afs.h | 2 ++
4 files changed, 43 insertions(+), 28 deletions(-)
diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 9068d5578a26..7bd659ad959e 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -350,7 +350,7 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode,
unsigned blkoff)
{
union afs_xdr_dirent *dire;
- unsigned offset, next, curr;
+ unsigned offset, next, curr, nr_slots;
size_t nlen;
int tmp;
@@ -363,13 +363,12 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode,
offset < AFS_DIR_SLOTS_PER_BLOCK;
offset = next
) {
- next = offset + 1;
-
/* skip entries marked unused in the bitmap */
if (!(block->hdr.bitmap[offset / 8] &
(1 << (offset % 8)))) {
_debug("ENT[%zu.%u]: unused",
blkoff / sizeof(union afs_xdr_dir_block), offset);
+ next = offset + 1;
if (offset >= curr)
ctx->pos = blkoff +
next * sizeof(union afs_xdr_dirent);
@@ -381,35 +380,39 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode,
nlen = strnlen(dire->u.name,
sizeof(*block) -
offset * sizeof(union afs_xdr_dirent));
+ if (nlen > AFSNAMEMAX - 1) {
+ _debug("ENT[%zu]: name too long (len %u/%zu)",
+ blkoff / sizeof(union afs_xdr_dir_block),
+ offset, nlen);
+ return afs_bad(dvnode, afs_file_error_dir_name_too_long);
+ }
_debug("ENT[%zu.%u]: %s %zu \"%s\"",
blkoff / sizeof(union afs_xdr_dir_block), offset,
(offset < curr ? "skip" : "fill"),
nlen, dire->u.name);
- /* work out where the next possible entry is */
- for (tmp = nlen; tmp > 15; tmp -= sizeof(union afs_xdr_dirent)) {
- if (next >= AFS_DIR_SLOTS_PER_BLOCK) {
- _debug("ENT[%zu.%u]:"
- " %u travelled beyond end dir block"
- " (len %u/%zu)",
- blkoff / sizeof(union afs_xdr_dir_block),
- offset, next, tmp, nlen);
- return afs_bad(dvnode, afs_file_error_dir_over_end);
- }
- if (!(block->hdr.bitmap[next / 8] &
- (1 << (next % 8)))) {
- _debug("ENT[%zu.%u]:"
- " %u unmarked extension (len %u/%zu)",
+ nr_slots = afs_dir_calc_slots(nlen);
+ next = offset + nr_slots;
+ if (next > AFS_DIR_SLOTS_PER_BLOCK) {
+ _debug("ENT[%zu.%u]:"
+ " %u extends beyond end dir block"
+ " (len %zu)",
+ blkoff / sizeof(union afs_xdr_dir_block),
+ offset, next, nlen);
+ return afs_bad(dvnode, afs_file_error_dir_over_end);
+ }
+
+ /* Check that the name-extension dirents are all allocated */
+ for (tmp = 1; tmp < nr_slots; tmp++) {
+ unsigned int ix = offset + tmp;
+ if (!(block->hdr.bitmap[ix / 8] & (1 << (ix % 8)))) {
+ _debug("ENT[%zu.u]:"
+ " %u unmarked extension (%u/%u)",
blkoff / sizeof(union afs_xdr_dir_block),
- offset, next, tmp, nlen);
+ offset, tmp, nr_slots);
return afs_bad(dvnode, afs_file_error_dir_unmarked_ext);
}
-
- _debug("ENT[%zu.%u]: ext %u/%zu",
- blkoff / sizeof(union afs_xdr_dir_block),
- next, tmp, nlen);
- next++;
}
/* skip if starts before the current position */
diff --git a/fs/afs/dir_edit.c b/fs/afs/dir_edit.c
index 2ffe09abae7f..f4600c1353ad 100644
--- a/fs/afs/dir_edit.c
+++ b/fs/afs/dir_edit.c
@@ -215,8 +215,7 @@ void afs_edit_dir_add(struct afs_vnode *vnode,
}
/* Work out how many slots we're going to need. */
- need_slots = round_up(12 + name->len + 1 + 4, AFS_DIR_DIRENT_SIZE);
- need_slots /= AFS_DIR_DIRENT_SIZE;
+ need_slots = afs_dir_calc_slots(name->len);
meta_page = kmap(page0);
meta = &meta_page->blocks[0];
@@ -393,8 +392,7 @@ void afs_edit_dir_remove(struct afs_vnode *vnode,
}
/* Work out how many slots we're going to discard. */
- need_slots = round_up(12 + name->len + 1 + 4, AFS_DIR_DIRENT_SIZE);
- need_slots /= AFS_DIR_DIRENT_SIZE;
+ need_slots = afs_dir_calc_slots(name->len);
meta_page = kmap(page0);
meta = &meta_page->blocks[0];
diff --git a/fs/afs/xdr_fs.h b/fs/afs/xdr_fs.h
index c926430fd08a..8ca868164507 100644
--- a/fs/afs/xdr_fs.h
+++ b/fs/afs/xdr_fs.h
@@ -58,7 +58,8 @@ union afs_xdr_dirent {
/* When determining the number of dirent slots needed to
* represent a directory entry, name should be assumed to be 16
* bytes, due to a now-standardised (mis)calculation, but it is
- * in fact 20 bytes in size.
+ * in fact 20 bytes in size. afs_dir_calc_slots() should be
+ * used for this.
*
* For names longer than (16 or) 20 bytes, extra slots should
* be annexed to this one using the extended_name format.
@@ -101,4 +102,15 @@ struct afs_xdr_dir_page {
union afs_xdr_dir_block blocks[AFS_DIR_BLOCKS_PER_PAGE];
};
+/*
+ * Calculate the number of dirent slots required for any given name length.
+ * The calculation is made assuming the part of the name in the first slot is
+ * 16 bytes, rather than 20, but this miscalculation is now standardised.
+ */
+static inline unsigned int afs_dir_calc_slots(size_t name_len)
+{
+ name_len++; /* NUL-terminated */
+ return 1 + ((name_len + 15) / AFS_DIR_DIRENT_SIZE);
+}
+
#endif /* XDR_FS_H */
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index 4eef374d4413..4a5cc8c64be3 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -231,6 +231,7 @@ enum afs_file_error {
afs_file_error_dir_bad_magic,
afs_file_error_dir_big,
afs_file_error_dir_missing_page,
+ afs_file_error_dir_name_too_long,
afs_file_error_dir_over_end,
afs_file_error_dir_small,
afs_file_error_dir_unmarked_ext,
@@ -488,6 +489,7 @@ enum afs_cb_break_reason {
EM(afs_file_error_dir_bad_magic, "DIR_BAD_MAGIC") \
EM(afs_file_error_dir_big, "DIR_BIG") \
EM(afs_file_error_dir_missing_page, "DIR_MISSING_PAGE") \
+ EM(afs_file_error_dir_name_too_long, "DIR_NAME_TOO_LONG") \
EM(afs_file_error_dir_over_end, "DIR_ENT_OVER_END") \
EM(afs_file_error_dir_small, "DIR_SMALL") \
EM(afs_file_error_dir_unmarked_ext, "DIR_UNMARKED_EXT") \
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