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uprobes: Fix the memory out of bound overwrite in copy_insn()

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1. copy_insn() doesn't look very nice, all calculations are
   confusing and it is not immediately clear why do we read
   the 2nd page first.

2. The usage of inode->i_size is wrong on 32-bit machines.

3. "Instruction at end of binary" logic is simply wrong, it
   doesn't handle the case when uprobe->offset > inode->i_size.

   In this case "bytes" overflows, and __copy_insn() writes to
   the memory outside of uprobe->arch.insn.

   Yes, uprobe_register() checks i_size_read(), but this file
   can be truncated after that. All i_size checks are racy, we
   do this only to catch the obvious mistakes.

Change copy_insn() to call __copy_insn() in a loop, simplify
and fix the bytes/nbytes calculations.

Note: we do not care if we read extra bytes after inode->i_size
if we got the valid page. This is fine because the task gets the
same page after page-fault, and arch_uprobe_analyze_insn() can't
know how many bytes were actually read anyway.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
This commit is contained in:
Oleg Nesterov 2013-11-07 19:41:57 +01:00
parent 70d7f98722
commit 2ded0980a6
1 changed files with 21 additions and 22 deletions
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43
kernel/events/uprobes.c
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@ -504,9 +504,8 @@ static bool consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
return ret;
}
static int
__copy_insn(struct address_space *mapping, struct file *filp, char *insn,
unsigned long nbytes, loff_t offset)
static int __copy_insn(struct address_space *mapping, struct file *filp,
void *insn, int nbytes, loff_t offset)
{
struct page *page;
@ -528,28 +527,28 @@ __copy_insn(struct address_space *mapping, struct file *filp, char *insn,
static int copy_insn(struct uprobe *uprobe, struct file *filp)
{
struct address_space *mapping;
unsigned long nbytes;
int bytes;
struct address_space *mapping = uprobe->inode->i_mapping;
loff_t offs = uprobe->offset;
void *insn = uprobe->arch.insn;
int size = MAX_UINSN_BYTES;
int len, err = -EIO;
nbytes = PAGE_SIZE - (uprobe->offset & ~PAGE_MASK);
mapping = uprobe->inode->i_mapping;
/* Copy only available bytes, -EIO if nothing was read */
do {
if (offs >= i_size_read(uprobe->inode))
break;
/* Instruction at end of binary; copy only available bytes */
if (uprobe->offset + MAX_UINSN_BYTES > uprobe->inode->i_size)
bytes = uprobe->inode->i_size - uprobe->offset;
else
bytes = MAX_UINSN_BYTES;
/* Instruction at the page-boundary; copy bytes in second page */
if (nbytes < bytes) {
int err = __copy_insn(mapping, filp, uprobe->arch.insn + nbytes,
bytes - nbytes, uprobe->offset + nbytes);
len = min_t(int, size, PAGE_SIZE - (offs & ~PAGE_MASK));
err = __copy_insn(mapping, filp, insn, len, offs);
if (err)
return err;
bytes = nbytes;
}
return __copy_insn(mapping, filp, uprobe->arch.insn, bytes, uprobe->offset);
break;
insn += len;
offs += len;
size -= len;
} while (size);
return err;
}
static int prepare_uprobe(struct uprobe *uprobe, struct file *file,