adfs: fix E+/F+ dir size > 2048 crashing kernel

Kernel crashes in fs/adfs module when accessing directories with a large
number of objects on mounted Acorn ADFS E+/F+ format discs (or images) as
the existing code writes off the end of the fixed array of struct
buffer_head pointers.

Additionally, each directory access that didn't crash would leak a buffer
as nr_buffers was not adjusted correctly for E+/F+ discs (was always left
as one less than required).

The patch fixes this by allocating a dynamically-sized set of struct
buffer_head pointers if necessary for the E+/F+ case (many directories
still do in fact fit in 2048 bytes) and sets the correct nr_buffers so
that all buffers are released.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=26072

Tested by tar'ing the contents of my RISC PC's E+ format 20Gb HDD which
contains a number of large directories that previously crashed the kernel.

Signed-off-by: Stuart Swales <stuart.swales.croftnuisk@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 84 insertions, 21 deletions

diff --git a/fs/adfs/adfs.h b/fs/adfs/adfs.h
index 2ff622f6f547..58588ddb178c 100644
--- a/fs/adfs/adfs.h
+++ b/fs/adfs/adfs.h
@@ -79,6 +79,10 @@ struct adfs_dir {
 
         int                     nr_buffers;
         struct buffer_head      *bh[4];
+
+        /* big directories need allocated buffers */
+        struct buffer_head      **bh_fplus;
+
         unsigned int            pos;
         unsigned int            parent_id;
 
diff --git a/fs/adfs/dir_fplus.c b/fs/adfs/dir_fplus.c
index 1796bb352d05..a7f41da8115b 100644
--- a/fs/adfs/dir_fplus.c
+++ b/fs/adfs/dir_fplus.c
@@ -8,6 +8,7 @@
  * published by the Free Software Foundation.
  */
 #include <linux/buffer_head.h>
+#include <linux/slab.h>
 #include "adfs.h"
 #include "dir_fplus.h"
 
@@ -22,30 +23,53 @@ adfs_fplus_read(struct super_block *sb, unsigned int id, unsigned int sz, struct
 
         dir->nr_buffers = 0;
 
+        /* start off using fixed bh set - only alloc for big dirs */
+        dir->bh_fplus = &dir->bh[0];
+
         block = __adfs_block_map(sb, id, 0);
         if (!block) {
                 adfs_error(sb, "dir object %X has a hole at offset 0", id);
                 goto out;
         }
 
-        dir->bh[0] = sb_bread(sb, block);
-        if (!dir->bh[0])
+        dir->bh_fplus[0] = sb_bread(sb, block);
+        if (!dir->bh_fplus[0])
                 goto out;
         dir->nr_buffers += 1;
 
-        h = (struct adfs_bigdirheader *)dir->bh[0]->b_data;
+        h = (struct adfs_bigdirheader *)dir->bh_fplus[0]->b_data;
         size = le32_to_cpu(h->bigdirsize);
         if (size != sz) {
-                printk(KERN_WARNING "adfs: adfs_fplus_read: directory header size\n"
-                                " does not match directory size\n");
+                printk(KERN_WARNING "adfs: adfs_fplus_read:"
+                                        " directory header size %X\n"
+                                        " does not match directory size %X\n",
+                                        size, sz);
         }
 
         if (h->bigdirversion[0] != 0 || h->bigdirversion[1] != 0 ||
             h->bigdirversion[2] != 0 || size & 2047 ||
-            h->bigdirstartname != cpu_to_le32(BIGDIRSTARTNAME))
+            h->bigdirstartname != cpu_to_le32(BIGDIRSTARTNAME)) {
+                printk(KERN_WARNING "adfs: dir object %X has"
+                                        " malformed dir header\n", id);
                 goto out;
+        }
 
         size >>= sb->s_blocksize_bits;
+        if (size > sizeof(dir->bh)/sizeof(dir->bh[0])) {
+                /* this directory is too big for fixed bh set, must allocate */
+                struct buffer_head **bh_fplus =
+                        kzalloc(size * sizeof(struct buffer_head *),
+                                GFP_KERNEL);
+                if (!bh_fplus) {
+                        adfs_error(sb, "not enough memory for"
+                                        " dir object %X (%d blocks)", id, size);
+                        goto out;
+                }
+                dir->bh_fplus = bh_fplus;
+                /* copy over the pointer to the block that we've already read */
+                dir->bh_fplus[0] = dir->bh[0];
+        }
+
         for (blk = 1; blk < size; blk++) {
                 block = __adfs_block_map(sb, id, blk);
                 if (!block) {
@@ -53,25 +77,44 @@ adfs_fplus_read(struct super_block *sb, unsigned int id, unsigned int sz, struct
                         goto out;
                 }
 
-                dir->bh[blk] = sb_bread(sb, block);
-                if (!dir->bh[blk])
+                dir->bh_fplus[blk] = sb_bread(sb, block);
+                if (!dir->bh_fplus[blk]) {
+                        adfs_error(sb,  "dir object %X failed read for"
+                                        " offset %d, mapped block %X",
+                                        id, blk, block);
                         goto out;
-                dir->nr_buffers = blk;
+                }
+
+                dir->nr_buffers += 1;
         }
 
-        t = (struct adfs_bigdirtail *)(dir->bh[size - 1]->b_data + (sb->s_blocksize - 8));
+        t = (struct adfs_bigdirtail *)
+                (dir->bh_fplus[size - 1]->b_data + (sb->s_blocksize - 8));
 
         if (t->bigdirendname != cpu_to_le32(BIGDIRENDNAME) ||
             t->bigdirendmasseq != h->startmasseq ||
-            t->reserved[0] != 0 || t->reserved[1] != 0)
+            t->reserved[0] != 0 || t->reserved[1] != 0) {
+                printk(KERN_WARNING "adfs: dir object %X has "
+                                        "malformed dir end\n", id);
                 goto out;
+        }
 
         dir->parent_id = le32_to_cpu(h->bigdirparent);
         dir->sb = sb;
         return 0;
+
 out:
-        for (i = 0; i < dir->nr_buffers; i++)
-                brelse(dir->bh[i]);
+        if (dir->bh_fplus) {
+                for (i = 0; i < dir->nr_buffers; i++)
+                        brelse(dir->bh_fplus[i]);
+
+                if (&dir->bh[0] != dir->bh_fplus)
+                        kfree(dir->bh_fplus);
+
+                dir->bh_fplus = NULL;
+        }
+
+        dir->nr_buffers = 0;
         dir->sb = NULL;
         return ret;
 }
@@ -79,7 +122,8 @@ out:
 static int
 adfs_fplus_setpos(struct adfs_dir *dir, unsigned int fpos)
 {
-        struct adfs_bigdirheader *h = (struct adfs_bigdirheader *)dir->bh[0]->b_data;
+        struct adfs_bigdirheader *h =
+                (struct adfs_bigdirheader *) dir->bh_fplus[0]->b_data;
         int ret = -ENOENT;
 
         if (fpos <= le32_to_cpu(h->bigdirentries)) {
@@ -102,21 +146,27 @@ dir_memcpy(struct adfs_dir *dir, unsigned int offset, void *to, int len)
         partial = sb->s_blocksize - offset;
 
         if (partial >= len)
-                memcpy(to, dir->bh[buffer]->b_data + offset, len);
+                memcpy(to, dir->bh_fplus[buffer]->b_data + offset, len);
         else {
                 char *c = (char *)to;
 
                 remainder = len - partial;
 
-                memcpy(c, dir->bh[buffer]->b_data + offset, partial);
-                memcpy(c + partial, dir->bh[buffer + 1]->b_data, remainder);
+                memcpy(c,
+                        dir->bh_fplus[buffer]->b_data + offset,
+                        partial);
+
+                memcpy(c + partial,
+                        dir->bh_fplus[buffer + 1]->b_data,
+                        remainder);
         }
 }
 
 static int
 adfs_fplus_getnext(struct adfs_dir *dir, struct object_info *obj)
 {
-        struct adfs_bigdirheader *h = (struct adfs_bigdirheader *)dir->bh[0]->b_data;
+        struct adfs_bigdirheader *h =
+                (struct adfs_bigdirheader *) dir->bh_fplus[0]->b_data;
         struct adfs_bigdirentry bde;
         unsigned int offset;
         int i, ret = -ENOENT;
@@ -160,7 +210,7 @@ adfs_fplus_sync(struct adfs_dir *dir)
         int i;
 
         for (i = dir->nr_buffers - 1; i >= 0; i--) {
-                struct buffer_head *bh = dir->bh[i];
+                struct buffer_head *bh = dir->bh_fplus[i];
                 sync_dirty_buffer(bh);
                 if (buffer_req(bh) && !buffer_uptodate(bh))
                         err = -EIO;
@@ -174,8 +224,17 @@ adfs_fplus_free(struct adfs_dir *dir)
 {
         int i;
 
-        for (i = 0; i < dir->nr_buffers; i++)
-                brelse(dir->bh[i]);
+        if (dir->bh_fplus) {
+                for (i = 0; i < dir->nr_buffers; i++)
+                        brelse(dir->bh_fplus[i]);
+
+                if (&dir->bh[0] != dir->bh_fplus)
+                        kfree(dir->bh_fplus);
+
+                dir->bh_fplus = NULL;
+        }
+
+        dir->nr_buffers = 0;
         dir->sb = NULL;
 }