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uprobes: Fix prepare_uprobe() race with itself

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install_breakpoint() is called under mm->mmap_sem, this protects
set_swbp() but not prepare_uprobe(). Two or more different tasks
can call install_breakpoint()->prepare_uprobe() at the same time,
this leads to numerous problems if UPROBE_COPY_INSN is not set.

Just for example, the second copy_insn() can corrupt the already
analyzed/fixuped uprobe->arch.insn and race with handle_swbp().

This patch simply adds uprobe->copy_mutex to serialize this code.
We could probably reuse ->consumer_rwsem, but this would mean that
consumer->handler() can not use mm->mmap_sem, not good.

Note: this is another temporary ugly hack until we move this logic
into uprobe_register().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
This commit is contained in:
Oleg Nesterov 2012-09-30 20:31:41 +02:00
parent cb9a19fe4a
commit 4710f05fd1
1 changed files with 8 additions and 0 deletions
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8
kernel/events/uprobes.c
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@ -89,6 +89,7 @@ struct uprobe {
struct rb_node rb_node; /* node in the rb tree */
atomic_t ref;
struct rw_semaphore consumer_rwsem;
struct mutex copy_mutex; /* TODO: kill me and UPROBE_COPY_INSN */
struct list_head pending_list;
struct uprobe_consumer *consumers;
struct inode *inode; /* Also hold a ref to inode */
@ -444,6 +445,7 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
uprobe->inode = igrab(inode);
uprobe->offset = offset;
init_rwsem(&uprobe->consumer_rwsem);
mutex_init(&uprobe->copy_mutex);
/* add to uprobes_tree, sorted on inode:offset */
cur_uprobe = insert_uprobe(uprobe);
@ -578,6 +580,10 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
if (uprobe->flags & UPROBE_COPY_INSN)
return ret;
mutex_lock(&uprobe->copy_mutex);
if (uprobe->flags & UPROBE_COPY_INSN)
goto out;
ret = copy_insn(uprobe, file);
if (ret)
goto out;
@ -598,6 +604,8 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
uprobe->flags |= UPROBE_COPY_INSN;
out:
mutex_unlock(&uprobe->copy_mutex);
return ret;
}