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[07/18] fs_context: fix double free of legacy_fs_context data

Message ID 20180708210154.10423-8-ebiggers3@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Eric Biggers July 8, 2018, 9:01 p.m. UTC 
From: Eric Biggers <ebiggers@google.com>

sys_fsmount() calls fc->ops->free() to free the data, zeroes
->fs_private, then proceeds to reuse the context.  But legacy_fs_context
doesn't use ->fs_private, so we need to handle zeroing it too; otherwise
there's a double free of legacy_fs_context::{legacy_data,secdata}.

Fixes: 8a2e54b8af88 ("vfs: Implement a filesystem superblock creation/configuration context")
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/fs_context.c | 3 +++
 1 file changed, 3 insertions(+)
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Patch

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 7a8d1ed34ae71..206256be9777e 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -504,6 +504,9 @@  static void legacy_fs_context_free(struct fs_context *fc)
 		kfree(ctx->legacy_data);
 		break;
 	}
+	/* This doesn't use fs_private, so need to manually zero for fsmount */
+	BUILD_BUG_ON(offsetof(struct legacy_fs_context, fc) != 0);
+	memset(fc + 1, 0, sizeof(*ctx) - sizeof(*fc));
 }
 
 /*