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Commit 2ded0980 authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

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



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: default avatarOleg Nesterov <oleg@redhat.com>
parent 70d7f987

kernel/events/uprobes.c

+21 −22
Original line number Diff line number Diff line
@@ -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;



	nbytes = PAGE_SIZE - (uprobe->offset & ~PAGE_MASK);

	mapping = uprobe->inode->i_mapping;

	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;



	/* 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;

	/* Copy only available bytes, -EIO if nothing was read */

	do {

		if (offs >= i_size_read(uprobe->inode))

			break;



	/* 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)

			break;



		insn += len;

		offs += len;

		size -= len;

	} while (size);



	return err;

		bytes = nbytes;

	}

	return __copy_insn(mapping, filp, uprobe->arch.insn, bytes, uprobe->offset);

}



static int prepare_uprobe(struct uprobe *uprobe, struct file *file,