use this patch with bash patch always_append_on_redirection.patch
this will fix 'dd' trying to seek past EOF into the file used for redirection while that file is open in O_APPEND mode

now(with this patch and bash patch!) it's this:
$ rm /tmp/out;echo abcdefghijklm | dd bs=5 seek=8 oflag=seek_bytes > /tmp/out ; stat --format=%s /tmp/out
dd: 'standard output': cannot seek: Illegal seek
0+0 records in
0+0 records out
0 bytes copied, 0.000102177 s, 0.0 kB/s
Actually written to disk: '0' bytes (-nan%).
0

before patch:
$ rm /tmp/out;echo abcdefghijklm | dd bs=5 seek=8 oflag=seek_bytes > /tmp/out ; stat --format=%s /tmp/out
2+1 records in
2+1 records out
14 bytes copied, 0.0001584 s, 88.4 kB/s
Actually written to disk: '14' bytes (100.00%). 
14

should be(if no bash patch was used):
$ rm /tmp/out;echo abcdefghijklm | dd bs=5 seek=8 oflag=seek_bytes > /tmp/out ; stat --format=%s /tmp/out
2+1 records in
2+1 records out
14 bytes copied, 0.000112444 s, 125 kB/s
Actually written to disk: '14' bytes (100.00%). 
22


diff --git a/fs/read_write.c b/fs/read_write.c
index 7458fccc59e1..e46c2997a158 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -88,6 +88,10 @@ generic_file_llseek_size(struct file *file, loff_t offset, int whence,
 {
 	switch (whence) {
 	case SEEK_END:
+		if ((file->f_flags & O_APPEND) && (offset > 0)) {
+			//tried to seek past EOF in O_APPEND mode will have no effect! so, this 'dd' will fail: echo abcdefghijklm | dd bs=5 seek=8 oflag=seek_bytes > /tmp/out ; stat --format=%s /tmp/out   ie. 14 written 14 bytes file size, instead of 22 bytes file size, if applied O_APPEND patch to bash's redirect operator, thus /tmp/out is O_APPEND mode! ok but actually it's not SEEK_END that's in effect here but SEEK_CUR instead!
+			return -ESPIPE; // ESPIPE 29 Illegal seek
+		}
 		offset += eof;
 		break;
 	case SEEK_CUR:
@@ -105,6 +109,13 @@ generic_file_llseek_size(struct file *file, loff_t offset, int whence,
 		 * like SEEK_SET.
 		 */
 		spin_lock(&file->f_lock);
+
+		if ((file->f_flags & O_APPEND) && (offset + file->f_pos > eof)) {
+			//tried to seek past EOF in O_APPEND mode will have no effect! so, this 'dd' will fail: echo abcdefghijklm | dd bs=5 seek=8 oflag=seek_bytes > /tmp/out ; stat --format=%s /tmp/out   ie. 14 written 14 bytes file size, instead of 22 bytes file size, if applied O_APPEND patch to bash's redirect operator, thus /tmp/out is O_APPEND mode! ok but actually it's not SEEK_END that's in effect here but SEEK_CUR instead!
+			spin_unlock(&file->f_lock);
+			return -ESPIPE; // ESPIPE 29 Illegal seek
+		}
+
 		offset = vfs_setpos(file, file->f_pos + offset, maxsize);
 		spin_unlock(&file->f_lock);
 		return offset;
@@ -127,6 +138,10 @@ generic_file_llseek_size(struct file *file, loff_t offset, int whence,
 		break;
 	}
 
+	if ((file->f_flags & O_APPEND) && (offset > eof)) {
+	  //tried to seek past EOF in O_APPEND mode will have no effect! so, this 'dd' will fail: echo abcdefghijklm | dd bs=5 seek=8 oflag=seek_bytes > /tmp/out ; stat --format=%s /tmp/out   ie. 14 written 14 bytes file size, instead of 22 bytes file size, if applied O_APPEND patch to bash's redirect operator, thus /tmp/out is O_APPEND mode! ok but actually it's not SEEK_END that's in effect here but SEEK_CUR instead!
+	  return -ESPIPE; // ESPIPE 29 Illegal seek
+	}
 	return vfs_setpos(file, offset, maxsize);
 }
 EXPORT_SYMBOL(generic_file_llseek_size);