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Fix atomicOTrunc implementation in fusefs.

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If FUSE connection does not support atomic O_TRUNC and application calls
open(O_TRUNC), FUSE should truncate the file *first* (without a file handle)
and then subsequently open the file with O_TRUNC filtered out.

We were truncating the file after open(). There were 2 issues with it:
1. We were using the inode's file handle, which may be invalid at this point
   because it is donated to the first FD (to save an open(2) RPC I believe)
   and that FD can close it.
2. The truncate() was being done with fhOptions.useFh = true. However,
   sometimes the file handle might be read-only causing truncate to fail.

Fixed both issues by moving the truncate above open() and making it not use any
file handles.

PiperOrigin-RevId: 567658664
This commit is contained in:
Ayush Ranjan
2023-09-22 10:35:43 -07:00
committed by gVisor bot
parent 19250b87ed
commit a277f53f25
1 changed files with 22 additions and 17 deletions
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pkg/sentry/fsimpl/fuse/inode.go
+22 -17
View File
@@ -292,6 +292,19 @@ func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentr
// FOPEN_KEEP_CACHE is the default flag for noOpen.
fd.OpenFlag = linux.FOPEN_KEEP_CACHE
truncateRegFile := opts.Flags&linux.O_TRUNC != 0 && i.filemode().FileType() == linux.S_IFREG
if truncateRegFile && (i.fh.new || !i.fs.conn.atomicOTrunc) {
// If the regular file needs to be truncated, but the connection doesn't
// support O_TRUNC or if we are optimizing away the Open RPC, then manually
// truncate the file *before* Open. As per libfuse, "If [atomic O_TRUNC is]
// disabled, and an application specifies O_TRUNC, fuse first calls
// truncate() and then open() with O_TRUNC filtered out.".
opts := vfs.SetStatOptions{Stat: linux.Statx{Size: 0, Mask: linux.STATX_SIZE}}
if err := i.setAttr(ctx, i.fs.VFSFilesystem(), auth.CredentialsFromContext(ctx), opts, fhOptions{useFh: false}); err != nil {
return nil, err
}
}
if i.fh.new {
fd.OpenFlag = i.fh.flags
fd.Fh = i.fh.handle
@@ -300,7 +313,7 @@ func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentr
// opening a directory.
} else if !i.fs.conn.noOpen || i.filemode().IsDir() {
in := linux.FUSEOpenIn{Flags: opts.Flags & ^uint32(linux.O_CREAT|linux.O_EXCL|linux.O_NOCTTY)}
// Truncating with SETATTR instead of O_TRUNC, so clear the flag.
// Clear O_TRUNC if the server doesn't support it.
if !i.fs.conn.atomicOTrunc {
in.Flags &= ^uint32(linux.O_TRUNC)
}
@@ -323,6 +336,14 @@ func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentr
}
fd.OpenFlag = out.OpenFlag
fd.Fh = out.Fh
// Open was successful. Update inode's size if atomicOTrunc && O_TRUNC.
if truncateRegFile && i.fs.conn.atomicOTrunc {
i.fs.conn.mu.Lock()
i.attrVersion.Store(i.fs.conn.attributeVersion.Add(1))
i.fs.conn.mu.Unlock()
i.size.Store(0)
i.touchCMtime()
}
}
}
if i.filemode().IsDir() {
@@ -338,22 +359,6 @@ func (i *inode) Open(ctx context.Context, rp *vfs.ResolvingPath, d *kernfs.Dentr
fd.Nonseekable = true
}
// If atomicOTrunc and O_TRUNC are set, just update the inode's version number
// and set its size to 0 since the truncation is handled by the FUSE daemon.
// Otherwise send a separate SETATTR to truncate the file size.
if opts.Flags&linux.O_TRUNC != 0 && i.filemode().FileType() == linux.S_IFREG {
if i.fs.conn.atomicOTrunc {
i.fs.conn.mu.Lock()
i.attrVersion.Store(i.fs.conn.attributeVersion.Add(1))
i.fs.conn.mu.Unlock()
i.size.Store(0)
i.touchCMtime()
} else {
opts := vfs.SetStatOptions{Stat: linux.Statx{Size: 0, Mask: linux.STATX_SIZE}}
i.setAttr(ctx, i.fs.VFSFilesystem(), auth.CredentialsFromContext(ctx), opts, fhOptions{useFh: true, fh: i.fh.handle})
}
}
if err := fd.vfsfd.Init(fdImpl, opts.Flags, rp.Mount(), d.VFSDentry(), fdOptions); err != nil {
return nil, err
}