forked from lix-project/lix
bd013b6f98
I was bitten one time too many by Python modifying the Nix store by creating *.pyc files when run as root. On Linux, we can prevent this by setting the immutable bit on files and directories (as in ‘chattr +i’). This isn't supported by all filesystems, so it's not an error if setting the bit fails. The immutable bit is cleared by the garbage collector before deleting a path. The only tricky aspect is in optimiseStore(), since it's forbidden to create hard links to an immutable file. Thus optimiseStore() temporarily clears the immutable bit before creating the link.
68 lines
1.4 KiB
C++
68 lines
1.4 KiB
C++
#include "config.h"
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#include "immutable.hh"
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#include "util.hh"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#if HAVE_LINUX_FS_H
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#include <linux/fs.h>
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#include <sys/ioctl.h>
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#include <errno.h>
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#endif
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namespace nix {
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void changeMutable(const Path & path, bool mut)
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{
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#if defined(FS_IOC_SETFLAGS) && defined(FS_IOC_GETFLAGS) && defined(FS_IMMUTABLE_FL)
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/* Don't even try if we're not root. One day we should support
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the CAP_LINUX_IMMUTABLE capability. */
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if (getuid() != 0) return;
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/* The O_NOFOLLOW is important to prevent us from changing the
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mutable bit on the target of a symlink (which would be a
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security hole). */
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AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_NOFOLLOW);
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if (fd == -1) {
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if (errno == ELOOP) return; // it's a symlink
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throw SysError(format("opening file `%1%'") % path);
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}
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unsigned int flags = 0, old;
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/* Silently ignore errors getting/setting the immutable flag so
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that we work correctly on filesystems that don't support it. */
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if (ioctl(fd, FS_IOC_GETFLAGS, &flags)) return;
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old = flags;
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if (mut) flags &= ~FS_IMMUTABLE_FL;
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else flags |= FS_IMMUTABLE_FL;
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if (old == flags) return;
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if (ioctl(fd, FS_IOC_SETFLAGS, &flags)) return;
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#endif
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}
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void makeImmutable(const Path & path)
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{
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changeMutable(path, false);
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}
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void makeMutable(const Path & path)
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{
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changeMutable(path, true);
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}
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}
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