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fs: ext4: Sign-extend tv_sec after ORing in epoch bits

PATCH In review Conrad Meyer 4 participants 4 messages Mar 30, 2014 – Apr 1, 2014 ext4 file system

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Conrad Meyer

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#0 lore raw

PATCH 1/1 fs: ext4: Sign-extend tv_sec after ORing in epoch bits

Fixes kernel.org bug #23732.

Background: ext4 stores time as a 34-bit quantity; 2 bits in some extra bits unneeded for nanoseconds in the inode, and 32 bits in the seconds field.

On systems with 64-bit time_t, the EXT4_*INODE_GET_XTIME() code incorrectly sign-extended the low 32-bits of the seconds quantity before ORing in the 2 "epoch" bits from nanoseconds.

This patch ORs in the 2 higher bits, then sign extends the 34-bit signed number to 64 bits.

Signed-off-by Conrad Meyer <[email protected]>

---
Patch against next-20140328.

Note, the on-disk format has always been written correctly. It was just interpreted incorrectly.

Repro:
Before:

$ touch -d 2038-01-31 test-123
$ sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"
$ ls -ld test-123
drwxrwxr-x 2 cmeyer cmeyer 4096 Dec 25  1901 test-123

After:

$ ls -ld test-123
drwxrwxr-x 2 cmeyer cmeyer 4096 Jan 31  2038 test-123

Thanks!

---
 fs/ext4/ext4.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
fs/ext4/ext4.h +12 -2
index f4f889e..07ee03d 100644
@@ -710,6 +710,8 @@ struct move_extent {
 #define EXT4_EPOCH_BITS 2
 #define EXT4_EPOCH_MASK ((1 << EXT4_EPOCH_BITS) - 1)
 #define EXT4_NSEC_MASK  (~0UL << EXT4_EPOCH_BITS)
+#define EXT4_EPOCH_SIGN (((1UL << (EXT4_EPOCH_BITS - 1)) << 16) << 16)
+#define EXT4_SIGN_EXT   (~((((1UL << EXT4_EPOCH_BITS) << 16) << 16) - 1))
 
 /*
  * Extended fields will fit into an inode if the filesystem was formatted

@@ -761,19 +763,23 @@ do {									       \
 
 #define EXT4_INODE_GET_XTIME(xtime, inode, raw_inode)			       \
 do {									       \
-	(inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
+	(inode)->xtime.tv_sec = (__u64)le32_to_cpu((raw_inode)->xtime);	       \
 	if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
 		ext4_decode_extra_time(&(inode)->xtime,			       \
 				       raw_inode->xtime ## _extra);	       \
 	else								       \
 		(inode)->xtime.tv_nsec = 0;				       \
+	if (sizeof((inode)->xtime.tv_sec) > 4) {			       \
+		if ((inode)->xtime.tv_sec & EXT4_EPOCH_SIGN)		       \
+			(inode)->xtime.tv_sec |= EXT4_SIGN_EXT;		       \
+	}								       \
 } while (0)
 
 #define EXT4_EINODE_GET_XTIME(xtime, einode, raw_inode)			       \
 do {									       \
 	if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime))		       \
 		(einode)->xtime.tv_sec = 				       \
-			(signed)le32_to_cpu((raw_inode)->xtime);	       \
+			(__u64)le32_to_cpu((raw_inode)->xtime);		       \
 	else								       \
 		(einode)->xtime.tv_sec = 0;				       \
 	if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime ## _extra))	       \

@@ -781,6 +787,10 @@ do {									       \
 				       raw_inode->xtime ## _extra);	       \
 	else								       \
 		(einode)->xtime.tv_nsec = 0;				       \
+	if (sizeof((einode)->xtime.tv_sec) > 4) {			       \
+		if ((einode)->xtime.tv_sec & EXT4_EPOCH_SIGN)		       \
+			(einode)->xtime.tv_sec |= EXT4_SIGN_EXT;	       \
+	}								       \
 } while (0)
 
 #define i_disk_version osd1.linux1.l_i_version
Signature · 1 line
1.9.0
#1 lore raw

Hmm,
I thought there was a separate patch to fix this a few months ago, that was "more correct" than this one? Did that not land?

Cheers, Andreas

Quoted 91 lines · Conrad Meyer

Fixes kernel.org bug #23732.

Background: ext4 stores time as a 34-bit quantity; 2 bits in some extra bits unneeded for nanoseconds in the inode, and 32 bits in the seconds field.

On systems with 64-bit time_t, the EXT4_*INODE_GET_XTIME() code incorrectly sign-extended the low 32-bits of the seconds quantity before ORing in the 2 "epoch" bits from nanoseconds.

This patch ORs in the 2 higher bits, then sign extends the 34-bit signed number to 64 bits.

Signed-off-by Conrad Meyer <[email protected]>

---
Patch against next-20140328.

Note, the on-disk format has always been written correctly. It was just interpreted incorrectly.

Repro:
Before:

$ touch -d 2038-01-31 test-123
$ sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"
$ ls -ld test-123
drwxrwxr-x 2 cmeyer cmeyer 4096 Dec 25  1901 test-123

After:

$ ls -ld test-123
drwxrwxr-x 2 cmeyer cmeyer 4096 Jan 31  2038 test-123

Thanks!
---
fs/ext4/ext4.h | 14 ++++++++++++--

1 file changed, 12 insertions(+), 2 deletions(-)
fs/ext4/ext4.h +12 -2
index f4f889e..07ee03d 100644
@@ -710,6 +710,8 @@ struct move_extent {
 #define EXT4_EPOCH_BITS 2
 #define EXT4_EPOCH_MASK ((1 << EXT4_EPOCH_BITS) - 1)
 #define EXT4_NSEC_MASK  (~0UL << EXT4_EPOCH_BITS)
+#define EXT4_EPOCH_SIGN (((1UL << (EXT4_EPOCH_BITS - 1)) << 16) << 16)
+#define EXT4_SIGN_EXT   (~((((1UL << EXT4_EPOCH_BITS) << 16) << 16) - 1))
 
 /*
 * Extended fields will fit into an inode if the filesystem was formatted

@@ -761,19 +763,23 @@ do {                                           \
 
 #define EXT4_INODE_GET_XTIME(xtime, inode, raw_inode)                   \
 do {                                           \
-    (inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
+    (inode)->xtime.tv_sec = (__u64)le32_to_cpu((raw_inode)->xtime);           \
   if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
       ext4_decode_extra_time(&(inode)->xtime,                   \
                      raw_inode->xtime ## _extra);           \
   else                                       \
       (inode)->xtime.tv_nsec = 0;                       \
+    if (sizeof((inode)->xtime.tv_sec) > 4) {                   \
+        if ((inode)->xtime.tv_sec & EXT4_EPOCH_SIGN)               \
+            (inode)->xtime.tv_sec |= EXT4_SIGN_EXT;               \
+    }                                       \
 } while (0)
 
 #define EXT4_EINODE_GET_XTIME(xtime, einode, raw_inode)                   \
 do {                                           \
   if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime))               \
       (einode)->xtime.tv_sec =                       \
-            (signed)le32_to_cpu((raw_inode)->xtime);           \
+            (__u64)le32_to_cpu((raw_inode)->xtime);               \
   else                                       \
       (einode)->xtime.tv_sec = 0;                       \
   if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime ## _extra))           \

@@ -781,6 +787,10 @@ do {                                           \
                      raw_inode->xtime ## _extra);           \
   else                                       \
       (einode)->xtime.tv_nsec = 0;                       \
+    if (sizeof((einode)->xtime.tv_sec) > 4) {                   \
+        if ((einode)->xtime.tv_sec & EXT4_EPOCH_SIGN)               \
+            (einode)->xtime.tv_sec |= EXT4_SIGN_EXT;           \
+    }                                       \
 } while (0)
 
 #define i_disk_version osd1.linux1.l_i_version
Signature · 1 line
1.9.0
#2 lore raw

The problem exists in mainline (v3.14) and linux-next (20140328), so it looks like it didn't land. Unless it's queued in an ext4 tree and didn't get selected for Linus for some reason?

Thanks,
Conrad

Quoted 96 lines · Andreas Dilger

Hmm,
I thought there was a separate patch to fix this a few months ago, that was "more correct" than this one? Did that not land?

Cheers, Andreas

Quoted 91 lines · Conrad Meyer

Fixes kernel.org bug #23732.

Background: ext4 stores time as a 34-bit quantity; 2 bits in some extra bits unneeded for nanoseconds in the inode, and 32 bits in the seconds field.

On systems with 64-bit time_t, the EXT4_*INODE_GET_XTIME() code incorrectly sign-extended the low 32-bits of the seconds quantity before ORing in the 2 "epoch" bits from nanoseconds.

This patch ORs in the 2 higher bits, then sign extends the 34-bit signed number to 64 bits.

Signed-off-by Conrad Meyer <[email protected]>

---
Patch against next-20140328.

Note, the on-disk format has always been written correctly. It was just interpreted incorrectly.

Repro:
Before:

$ touch -d 2038-01-31 test-123
$ sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"
$ ls -ld test-123
drwxrwxr-x 2 cmeyer cmeyer 4096 Dec 25  1901 test-123

After:

$ ls -ld test-123
drwxrwxr-x 2 cmeyer cmeyer 4096 Jan 31  2038 test-123

Thanks!
---
fs/ext4/ext4.h | 14 ++++++++++++--

1 file changed, 12 insertions(+), 2 deletions(-)
fs/ext4/ext4.h +12 -3
index f4f889e..07ee03d 100644
@@ -710,6 +710,8 @@ struct move_extent {
 #define EXT4_EPOCH_BITS 2
 #define EXT4_EPOCH_MASK ((1 << EXT4_EPOCH_BITS) - 1)
 #define EXT4_NSEC_MASK  (~0UL << EXT4_EPOCH_BITS)
+#define EXT4_EPOCH_SIGN (((1UL << (EXT4_EPOCH_BITS - 1)) << 16) << 16)
+#define EXT4_SIGN_EXT   (~((((1UL << EXT4_EPOCH_BITS) << 16) << 16) - 1))
 
 /*
 * Extended fields will fit into an inode if the filesystem was formatted

@@ -761,19 +763,23 @@ do {                                           \
 
 #define EXT4_INODE_GET_XTIME(xtime, inode, raw_inode)                   \
 do {                                           \
-    (inode)->xtime.tv_sec = (signed)le32_to_cpu((raw_inode)->xtime);       \
+    (inode)->xtime.tv_sec = (__u64)le32_to_cpu((raw_inode)->xtime);           \
   if (EXT4_FITS_IN_INODE(raw_inode, EXT4_I(inode), xtime ## _extra))     \
       ext4_decode_extra_time(&(inode)->xtime,                   \
                      raw_inode->xtime ## _extra);           \
   else                                       \
       (inode)->xtime.tv_nsec = 0;                       \
+    if (sizeof((inode)->xtime.tv_sec) > 4) {                   \
+        if ((inode)->xtime.tv_sec & EXT4_EPOCH_SIGN)               \
+            (inode)->xtime.tv_sec |= EXT4_SIGN_EXT;               \
+    }                                       \
 } while (0)
 
 #define EXT4_EINODE_GET_XTIME(xtime, einode, raw_inode)                   \
 do {                                           \
   if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime))               \
       (einode)->xtime.tv_sec =                       \
-            (signed)le32_to_cpu((raw_inode)->xtime);           \
+            (__u64)le32_to_cpu((raw_inode)->xtime);               \
   else                                       \
       (einode)->xtime.tv_sec = 0;                       \
   if (EXT4_FITS_IN_INODE(raw_inode, einode, xtime ## _extra))           \

@@ -781,6 +787,10 @@ do {                                           \
                      raw_inode->xtime ## _extra);           \
   else                                       \
       (einode)->xtime.tv_nsec = 0;                       \
+    if (sizeof((einode)->xtime.tv_sec) > 4) {                   \
+        if ((einode)->xtime.tv_sec & EXT4_EPOCH_SIGN)               \
+            (einode)->xtime.tv_sec |= EXT4_SIGN_EXT;           \
+    }                                       \
 } while (0)
 
 #define i_disk_version osd1.linux1.l_i_version
--

1.9.0

maintainer
#3 lore raw
Quoted 3 lines · Conrad Meyer

The problem exists in mainline (v3.14) and linux-next (20140328), so it looks like it didn't land. Unless it's queued in an ext4 tree and didn't get selected for Linus for some reason?

There were some proposals for a different encoding that would be better, that would have required some e2fsprogs changes. Since this is a long range problem (that doesn't hit until 2038) it's not been high priority to deal with, but I haven't forgotten it. I've just had higher priority items on my todo list.

The huge long thread can be found here:

    http://thread.gmane.org/gmane.comp.file-systems.ext4/40978

What this is blocked on is I wanted to have some better ways of setting times using the old and the proposed new encoding convention, so we could have proper regression tests for the changes in e2fsck. That way we can make sure the right thing really happens with 32-bit kernels, 64-bit kernels, 32-bit e2fsprogs, 64-bit e2fsprogs, etc., with file systems using both the old and the newer encoding.

(Yes, I'm paranoid that way. Regression tests are _important_.)

- Ted