Merge tag 'afs-fixes-04012021' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull AFS fixes from David Howells:
 "Two fixes.

  The first is the fix for the strnlen() array limit check and the
  second fixes the calculation of the number of dirent records used to
  represent any particular filename length"

* tag 'afs-fixes-04012021' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  afs: Fix directory entry size calculation
  afs: Work around strnlen() oops with CONFIG_FORTIFIED_SOURCE=y

3 files changed, 49 insertions, 31 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 94f1f398eefa..8ca868164507 100644
--- a/fs/afs/xdr_fs.h
+++ b/fs/afs/xdr_fs.h
@@ -54,10 +54,16 @@ union afs_xdr_dirent {
 		__be16		hash_next;
 		__be32		vnode;
 		__be32		unique;
-		u8		name[16];
-		u8		overflow[4];	/* if any char of the name (inc
-						 * NUL) reaches here, consume
-						 * the next dirent too */
+		u8		name[];
+		/* 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.  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.
+		 */
 	} u;
 	u8			extended_name[32];
 } __packed;
@@ -96,4 +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 */