[PATCH v3 5/5] fs/fshelp: Avoid possible NULL pointer deference

[Andrew Hamilton <adhamilt@gmail.com>]

Avoid attempting to defererence a NULL pointer to call read_symlink when
the given filesystem does not provide a read_symlink function. This could
be triggered if the calling filesystem had a file marked as a symlink.
This appears possible for HFS and was observed during fuzzing of NTFS.

Signed-off-by: Andrew Hamilton <adhamilt@gmail.com>
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/fs/fshelp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/grub-core/fs/fshelp.c b/grub-core/fs/fshelp.c
index cb41934b4..15278fb80 100644
--- a/grub-core/fs/fshelp.c
+++ b/grub-core/fs/fshelp.c
@@ -226,7 +226,10 @@ find_file (char *currpath,
 	    return grub_error (GRUB_ERR_SYMLINK_LOOP,
 			       N_("too deep nesting of symlinks"));
 
-	  symlink = read_symlink (ctx->currnode->node);
+	  if (read_symlink != NULL)
+	    symlink = read_symlink (ctx->currnode->node);
+	  else
+	    return grub_error (GRUB_ERR_BAD_FS, "read_symlink is NULL");
 
 	  if (!symlink)
 	    return grub_errno;
-- 
2.39.5


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