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Merge pull request #1645 from twhitehead/stat-race

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Fix (highly unlikely) race condition in readLink
This commit is contained in:
Eelco Dolstra 2017-11-20 17:32:27 +01:00 committed by GitHub
commit 72804dc0bd
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1 changed files with 11 additions and 12 deletions
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23
src/libutil/util.cc
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@ -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);
}
}