From: Darrick J. Wong <djwong@xxxxxxxxxx>
There's a major discrepancy in the function that computes directory entry
hashes for filesystems that have ASCII case-insensitive lookups enabled.
The root of this is that the kernel and glibc's tolower implementations
have differing behavior for extended ASCII accented characters. I wrote
a program to spit out characters for which the tolower() return value is
different from the input:
glibc tolower:
65:A 66:B 67:C 68:D 69:E 70:F 71:G 72:H 73:I 74:J 75:K 76:L 77:M 78:N
79:O 80:P 81:Q 82:R 83:S 84:T 85:U 86:V 87:W 88:X 89:Y 90:Z
kernel tolower:
65:A 66:B 67:C 68:D 69:E 70:F 71:G 72:H 73:I 74:J 75:K 76:L 77:M 78:N
79:O 80:P 81:Q 82:R 83:S 84:T 85:U 86:V 87:W 88:X 89:Y 90:Z 192:À 193:Á
194:Â 195:Ã 196:Ä 197:Å 198:Æ 199:Ç 200:È 201:É 202:Ê 203:Ë 204:Ì 205:Í
206:Î 207:Ï 208:Ð 209:Ñ 210:Ò 211:Ó 212:Ô 213:Õ 214:Ö 215:× 216:Ø 217:Ù
218:Ú 219:Û 220:Ü 221:Ý 222:Þ
Which means that the kernel and userspace do not agree on the hash value
for a directory filename that contains those higher values. The hash
values are written into the leaf index block of directories that are
larger than two blocks in size, which means that xfs_repair will flag
these directories as having corrupted hash indexes and rewrite the index
with hash values that the kernel now will not recognize.
Because the ascii-ci feature is not frequently enabled and the kernel
touches filesystems far more frequently than xfs_repair does, fix this
by encoding the kernel's toupper predicate and tolower functions into
libxfs. This makes userspace's behavior consistent with the kernel.
Found by auditing obfuscate_name in xfs_metadump as part of working on
parent pointers, wondering how it could possibly work correctly with ci
filesystems, writing a test tool to create a directory with
hash-colliding names, and watching xfs_repair flag it.
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
fs/xfs/libxfs/xfs_dir2.c | 4 ++--
fs/xfs/libxfs/xfs_dir2.h | 20 ++++++++++++++++++++
2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/libxfs/xfs_dir2.c b/fs/xfs/libxfs/xfs_dir2.c
index 92bac3373f1f..eb3187ee977d 100644
--- a/fs/xfs/libxfs/xfs_dir2.c
+++ b/fs/xfs/libxfs/xfs_dir2.c
@@ -64,7 +64,7 @@ xfs_ascii_ci_hashname(
int i;
for (i = 0, hash = 0; i < name->len; i++)
- hash = tolower(name->name[i]) ^ rol32(hash, 7);
+ hash = xfs_ascii_ci_tolower(name->name[i]) ^ rol32(hash, 7);
return hash;
}
@@ -85,7 +85,7 @@ xfs_ascii_ci_compname(
for (i = 0; i < len; i++) {
if (args->name[i] == name[i])
continue;
- if (tolower(args->name[i]) != tolower(name[i]))
+ if (xfs_ascii_ci_tolower(args->name[i]) != xfs_ascii_ci_tolower(name[i]))
return XFS_CMP_DIFFERENT;
result = XFS_CMP_CASE;
}
diff --git a/fs/xfs/libxfs/xfs_dir2.h b/fs/xfs/libxfs/xfs_dir2.h
index dd39f17dd9a9..2772fd53279c 100644
--- a/fs/xfs/libxfs/xfs_dir2.h
+++ b/fs/xfs/libxfs/xfs_dir2.h
@@ -248,4 +248,24 @@ unsigned int xfs_dir3_data_end_offset(struct xfs_da_geometry *geo,
struct xfs_dir2_data_hdr *hdr);
bool xfs_dir2_namecheck(const void *name, size_t length);
+static inline bool
+xfs_ascii_ci_isupper(unsigned char c)
+{
+ if (c >= 0x41 && c <= 0x5a) /* A-Z */
+ return true;
+ if (c >= 0xc0 && c <= 0xd6) /* latin A-O with accents */
+ return true;
+ if (c >= 0xd8 && c <= 0xde) /* latin O-Y with accents */
+ return true;
+ return false;
+}
+
+static inline unsigned char
+xfs_ascii_ci_tolower(unsigned char c)
+{
+ if (xfs_ascii_ci_isupper(c))
+ c -= 'A' - 'a';
+ return c;
+}
+
#endif /* __XFS_DIR2_H__ */
