uprobes: Fix prepare_uprobe() race with itself
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>
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@ -89,6 +89,7 @@ struct uprobe {
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struct rb_node rb_node; /* node in the rb tree */
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atomic_t ref;
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struct rw_semaphore consumer_rwsem;
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struct mutex copy_mutex; /* TODO: kill me and UPROBE_COPY_INSN */
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struct list_head pending_list;
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struct uprobe_consumer *consumers;
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struct inode *inode; /* Also hold a ref to inode */
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@ -444,6 +445,7 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
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uprobe->inode = igrab(inode);
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uprobe->offset = offset;
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init_rwsem(&uprobe->consumer_rwsem);
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mutex_init(&uprobe->copy_mutex);
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/* add to uprobes_tree, sorted on inode:offset */
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cur_uprobe = insert_uprobe(uprobe);
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@ -578,6 +580,10 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
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if (uprobe->flags & UPROBE_COPY_INSN)
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return ret;
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mutex_lock(&uprobe->copy_mutex);
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if (uprobe->flags & UPROBE_COPY_INSN)
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goto out;
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ret = copy_insn(uprobe, file);
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if (ret)
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goto out;
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@ -598,6 +604,8 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
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uprobe->flags |= UPROBE_COPY_INSN;
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out:
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mutex_unlock(&uprobe->copy_mutex);
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return ret;
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}
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