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authorEelco Dolstra <eelco.dolstra@logicblox.com>2017-11-20T16·32+0100
committerGitHub <noreply@github.com>2017-11-20T16·32+0100
commit72804dc0bdc560c6f7db0fa638403fdddbe692fd (patch)
tree4a50dc4c587ddeb1f263aadfe70f1614d3cfc361
parent7474ac871b73bd4e739a547b4870b33d625d4c70 (diff)
parent07d2c6d213660e178fcdf128ea6f1f36d9d8a85d (diff)
Merge pull request #1645 from twhitehead/stat-race
Fix (highly unlikely) race condition in readLink
-rw-r--r--src/libutil/util.cc23
1 files changed, 11 insertions, 12 deletions
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index f56153cd4a8a..96c0cd78383d 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -216,18 +216,17 @@ bool pathExists(const Path & path)
 Path readLink(const Path & path)
 {
     checkInterrupt();
-    struct stat st = lstat(path);
-    if (!S_ISLNK(st.st_mode))
-        throw Error(format("'%1%' is not a symlink") % path);
-    auto bufSize = std::max(st.st_size, (off_t) PATH_MAX + 1);
-    char buf[bufSize];
-    ssize_t rlsize = readlink(path.c_str(), buf, bufSize);
-    if (rlsize == -1)
-        throw SysError(format("reading symbolic link '%1%'") % path);
-    else if (rlsize > bufSize)
-        throw Error(format("symbolic link '%1%' size overflow %2% > %3%")
-            % path % rlsize % bufSize);
-    return string(buf, rlsize);
+    for (ssize_t bufSize = PATH_MAX/4; true; bufSize += bufSize/2) {
+        char buf[bufSize];
+        ssize_t rlSize = readlink(path.c_str(), buf, bufSize);
+        if (rlSize == -1)
+            if (errno == EINVAL)
+                throw Error(format("'%1%' is not a symlink") % path);
+            else
+                throw SysError(format("reading symbolic link '%1%'") % path);
+        else if (rlSize < bufSize)
+            return string(buf, rlSize);
+    }
 }