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freevxfs: refactor readdir and lookup code
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This change fixes also a buffer overflow which was caused by
accessing address space beyond mapped page

Signed-off-by: Krzysztof Błaszkowski <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
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@kb-01
kb-01 authored and Christoph Hellwig committed Jun 12, 2016
1 parent f2fe2fa commit 12495ea
Showing 1 changed file with 108 additions and 125 deletions.
233 changes: 108 additions & 125 deletions fs/freevxfs/vxfs_lookup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -62,35 +62,6 @@ const struct file_operations vxfs_dir_operations = {
.iterate_shared = vxfs_readdir,
};

static inline u_long
dir_blocks(struct inode *ip)
{
u_long bsize = ip->i_sb->s_blocksize;
return (ip->i_size + bsize - 1) & ~(bsize - 1);
}

/*
* NOTE! unlike strncmp, vxfs_match returns 1 for success, 0 for failure.
*
* len <= VXFS_NAMELEN and de != NULL are guaranteed by caller.
*/
static inline int
vxfs_match(struct vxfs_sb_info *sbi, int len, const char *const name,
struct vxfs_direct *de)
{
if (len != fs16_to_cpu(sbi, de->d_namelen))
return 0;
if (!de->d_ino)
return 0;
return !memcmp(name, de->d_name, len);
}

static inline struct vxfs_direct *
vxfs_next_entry(struct vxfs_sb_info *sbi, struct vxfs_direct *de)
{
return ((struct vxfs_direct *)
((char *)de + fs16_to_cpu(sbi, de->d_reclen)));
}

/**
* vxfs_find_entry - find a mathing directory entry for a dentry
Expand All @@ -109,53 +80,64 @@ vxfs_next_entry(struct vxfs_sb_info *sbi, struct vxfs_direct *de)
static struct vxfs_direct *
vxfs_find_entry(struct inode *ip, struct dentry *dp, struct page **ppp)
{
struct vxfs_sb_info *sbi = VXFS_SBI(ip->i_sb);
u_long npages, page, nblocks, pblocks, block;
u_long bsize = ip->i_sb->s_blocksize;
const char *name = dp->d_name.name;
int namelen = dp->d_name.len;

npages = dir_pages(ip);
nblocks = dir_blocks(ip);
pblocks = VXFS_BLOCK_PER_PAGE(ip->i_sb);

for (page = 0; page < npages; page++) {
caddr_t kaddr;
struct page *pp;
u_long bsize = ip->i_sb->s_blocksize;
const char *name = dp->d_name.name;
int namelen = dp->d_name.len;
loff_t limit = VXFS_DIRROUND(ip->i_size);
struct vxfs_direct *de_exit = NULL;
loff_t pos = 0;
struct vxfs_sb_info *sbi = VXFS_SBI(ip->i_sb);

while (pos < limit) {
struct page *pp;
char *kaddr;
int pg_ofs = pos & ~PAGE_MASK;

pp = vxfs_get_page(ip->i_mapping, page);
pp = vxfs_get_page(ip->i_mapping, pos >> PAGE_SHIFT);
if (IS_ERR(pp))
continue;
kaddr = (caddr_t)page_address(pp);

for (block = 0; block <= nblocks && block <= pblocks; block++) {
caddr_t baddr, limit;
struct vxfs_dirblk *dbp;
struct vxfs_direct *de;

baddr = kaddr + (block * bsize);
limit = baddr + bsize - VXFS_DIRLEN(1);

dbp = (struct vxfs_dirblk *)baddr;
de = (struct vxfs_direct *)
(baddr + VXFS_DIRBLKOV(sbi, dbp));

for (; (caddr_t)de <= limit;
de = vxfs_next_entry(sbi, de)) {
if (!de->d_reclen)
break;
if (!de->d_ino)
continue;
if (vxfs_match(sbi, namelen, name, de)) {
*ppp = pp;
return (de);
}
return NULL;
kaddr = (char *)page_address(pp);

while (pg_ofs < PAGE_SIZE && pos < limit) {
struct vxfs_direct *de;

if ((pos & (bsize - 1)) < 4) {
struct vxfs_dirblk *dbp =
(struct vxfs_dirblk *)
(kaddr + (pos & ~PAGE_MASK));
int overhead = VXFS_DIRBLKOV(sbi, dbp);

pos += overhead;
pg_ofs += overhead;
}
de = (struct vxfs_direct *)(kaddr + pg_ofs);

if (!de->d_reclen) {
pos += bsize - 1;
pos &= ~(bsize - 1);
break;
}

pg_ofs += fs16_to_cpu(sbi, de->d_reclen);
pos += fs16_to_cpu(sbi, de->d_reclen);
if (!de->d_ino)
continue;

if (namelen != fs16_to_cpu(sbi, de->d_namelen))
continue;
if (!memcmp(name, de->d_name, namelen)) {
*ppp = pp;
de_exit = de;
break;
}
}
vxfs_put_page(pp);
if (!de_exit)
vxfs_put_page(pp);
else
break;
}

return NULL;
return de_exit;
}

/**
Expand Down Expand Up @@ -238,80 +220,81 @@ vxfs_readdir(struct file *fp, struct dir_context *ctx)
{
struct inode *ip = file_inode(fp);
struct super_block *sbp = ip->i_sb;
struct vxfs_sb_info *sbi = VXFS_SBI(sbp);
u_long bsize = sbp->s_blocksize;
u_long page, npages, block, pblocks, nblocks, offset;
loff_t pos;

loff_t pos, limit;
struct vxfs_sb_info *sbi = VXFS_SBI(sbp);

if (ctx->pos == 0) {
if (!dir_emit_dot(fp, ctx))
return 0;
ctx->pos = 1;
goto out;
ctx->pos++;
}
if (ctx->pos == 1) {
if (!dir_emit(ctx, "..", 2, VXFS_INO(ip)->vii_dotdot, DT_DIR))
return 0;
ctx->pos = 2;
goto out;
ctx->pos++;
}
pos = ctx->pos - 2;

if (pos > VXFS_DIRROUND(ip->i_size))
return 0;

npages = dir_pages(ip);
nblocks = dir_blocks(ip);
pblocks = VXFS_BLOCK_PER_PAGE(sbp);
limit = VXFS_DIRROUND(ip->i_size);
if (ctx->pos > limit)
goto out;

page = pos >> PAGE_SHIFT;
offset = pos & ~PAGE_MASK;
block = (u_long)(pos >> sbp->s_blocksize_bits) % pblocks;
pos = ctx->pos & ~3L;

for (; page < npages; page++, block = 0) {
char *kaddr;
struct page *pp;
while (pos < limit) {
struct page *pp;
char *kaddr;
int pg_ofs = pos & ~PAGE_MASK;
int rc = 0;

pp = vxfs_get_page(ip->i_mapping, page);
pp = vxfs_get_page(ip->i_mapping, pos >> PAGE_SHIFT);
if (IS_ERR(pp))
continue;
return -ENOMEM;

kaddr = (char *)page_address(pp);

for (; block <= nblocks && block <= pblocks; block++) {
char *baddr, *limit;
struct vxfs_dirblk *dbp;
struct vxfs_direct *de;
while (pg_ofs < PAGE_SIZE && pos < limit) {
struct vxfs_direct *de;

baddr = kaddr + (block * bsize);
limit = baddr + bsize - VXFS_DIRLEN(1);

dbp = (struct vxfs_dirblk *)baddr;
de = (struct vxfs_direct *)
(offset ?
(kaddr + offset) :
(baddr + VXFS_DIRBLKOV(sbi, dbp)));

for (; (char *)de <= limit;
de = vxfs_next_entry(sbi, de)) {
if (!de->d_reclen)
break;
if (!de->d_ino)
continue;

offset = (char *)de - kaddr;
ctx->pos = ((page << PAGE_SHIFT) | offset) + 2;
if (!dir_emit(ctx, de->d_name,
fs16_to_cpu(sbi, de->d_namelen),
fs32_to_cpu(sbi, de->d_ino),
DT_UNKNOWN)) {
vxfs_put_page(pp);
return 0;
}
if ((pos & (bsize - 1)) < 4) {
struct vxfs_dirblk *dbp =
(struct vxfs_dirblk *)
(kaddr + (pos & ~PAGE_MASK));
int overhead = VXFS_DIRBLKOV(sbi, dbp);

pos += overhead;
pg_ofs += overhead;
}
de = (struct vxfs_direct *)(kaddr + pg_ofs);

if (!de->d_reclen) {
pos += bsize - 1;
pos &= ~(bsize - 1);
break;
}

pg_ofs += fs16_to_cpu(sbi, de->d_reclen);
pos += fs16_to_cpu(sbi, de->d_reclen);
if (!de->d_ino)
continue;

rc = dir_emit(ctx, de->d_name,
fs16_to_cpu(sbi, de->d_namelen),
fs32_to_cpu(sbi, de->d_ino),
DT_UNKNOWN);
if (!rc) {
/* the dir entry was not read, fix pos. */
pos -= fs16_to_cpu(sbi, de->d_reclen);
break;
}
offset = 0;
}
vxfs_put_page(pp);
offset = 0;
if (!rc)
break;
}
ctx->pos = ((page << PAGE_SHIFT) | offset) + 2;

ctx->pos = pos | 2;

out:
return 0;
}

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